May I offer a suggestion? This is one of the features of the REL line of subwoofers, they provide options to connect directly to the amplifier speaker posts to allow a seamless crossover via high level connection:
https://relsupport.zendesk.com/hc/en-us/articles/115004486987-What-is-a-High-Level-Connection-
Take a look, it is one of the main reasons for my own use of their subwoofers.
Thanks for the suggestion but my speakers (and sub) are powered, I need balanced line level to feed them individually.
Seems to me you would benefit from a simple RCA-to-XLR converter box (stereo). The idea is that no D-to-A or A-to-D is involved: youāre simply taking RCA L/R interconnect in & XLR L/R interconnect (I believe you can also reverse them and output RCA from XLR in).
Itās important that the box I recommend has a volume pot for each channel. Important as the XLR coming out (like all balanced signal) is more dB than the RCA coming in. This helps you adjust system gain somewhatā¦
I picked up a used Aphex 124a after reading that it was used in many music studios & well regarded for sonics & bulletproofāness. Mine certainly verified all that. Iām no longer using it, but keep it around just in caseā¦
Hereās a link to one F.S. on ebay (these arenāt hard to find):
I would still need to add in a crossover at some point after that. I was running a similar set up with my Tannoy system in the kitchen, using RDL transformers and a Rane crossover.
Yupā¦same old problem remains.
Hereās a potential solution at reasonable price. Note the XM-9 is a fixed value crossover: 2 channels, 1 input/2 outputs (high-pass; low-pass). All RCA. If you want to change crossover points, you swap out little crossover cards, one per channel. The one in ad below comes w/3 crossover cards (60 Hz; 80 Hz; 100 Hz), probably all you would need.
You can also buy these new configured for XLR in/out & other goodies.
Yes, that is a possible solution but I donāt think it would be an improvement over my current set up (the BLU-160 is a decent piece of kit).
I would just like to do all the dividing of signals while still in the digital domain, before any DAC.
Another option is to use a BLU-USB which allows me to feed Blu-Link (BSS audio over network) directly into the BLU-160 but it is a 300ā¬ solution that limits me to PC only, which is fine for me but not my other half.
I could also add a Dante card but it is the same thing (unless anyone knows of a Dante card for the Pi?).
My solution in the office, where I have a similar set up, is to use VB-Audio Voicemeter which lets me use multiple DAC on my PC. I use one DAC for mains and one for subs (with crossover done in Voicemeter). But once again, PC limited and not wife friendly 
It may just be that I donāt understand your system. But Iām confused by you wanting to do crossover in digital realm vs analog, given this:
āThe issue with this is that I am using the DAC in the Marantz to output RCA, then the BSS is doing ADC before processing, then DAC out of the BSS. Thereās a lot of DAC/ADC/DAC going onā
?
Sorry, I probably didnāt explain very well. I would remove the Marantz and the BSS from the set up.
My aim would be:
Sources > DAC > Speakers (and sub).
So the crossover and any EQ would be done in the DAC before becoming analog.
You all have such beautiful, clean setups. I canāt show mine well in photographs for several reasons. Some 20 years ago, I was looking for a spot to install most of my equipment. Iād been thinking about converting a small closet, but our 1940ās era home is short on closet space. A local stereo store was having a sale, and I got their floor model TV/stereo cabinet. Itās about 6.5 feet (2M) tall, and wide enough for a 42 inch TV. It closes up, so you donāt see the TV all the time. Itās in a living room corner - the piano is in the other corner.
This cabinet houses not only the TV, but cable box, Blu-Ray player, Rotel CD player, the VPI turntable, some CDs and vinyl, the Wired 4 Sound STI 1000 integrated amp, Musical Fidelity phono preamp, Teac DAC, Monster Sound power conditioner/surge protector, and Sonos Port. On top is a soundbar for the TV. A Bluetooth sub that goes with the TV is nearby.
Snaking around the corner coming out of the cabinet are some Cardas Litz cables to my Rectilinear 3 Highboy speakers on either side of the fireplace, which is on the long side of the rectangular 13 x 25 foot room. The Highboys lack the proper grilles, so I made some from black grille metal, had them flanged properly, so they fit correctly. So the speakers are a nice walnut veneer with black fronts.
I will get a few photos up of my 2.1 setup soon!
I like my KEFs. Not anywhere near high end but I doubt I could hear the difference. If I had money to burn
I would like to try some of the new KEF LS50 or possibly the powered versions. I could stream my Amazon Ultra HD music directly.
Not to brag (OK, just a little) those guitars in total are worth a lot more than my entire entertainment set up.
HEDD founder Klaus Heinz introduced the new monitor lineup recently. Including an 8 and 12 inch subwoofer
super interesting for me.
Canāt wait to try the new 07 II with the 8inch sub.
Yeah I saw this and got super excited. I still need to get some of their speakers in. Ever since hearing some of them in New York this year, their speaker lineup has been on my radar. Not sure how suitable they are for my office, but maybe the smallest ones haha.
The first gen 20 is highly recommended by some electronic music producing buddies/family
Hope for a used first gen HEDD set- could be more in my budget
It would be very cool to hear these!
Oh if only we could do that thing we used to do called travelā¦
Yes and or ā¦ visit our local dealer / go to a show like munich high endā¦
The local dealer here in Hong Kong sent a message regarding a sale on Type 05 and 07. I guess they need to clear them off their inventory because of the MK2. The Type 20 does look the most attractive but it would take quite a bite out of the wallet. I also have my eyes on the ATC as well but those actives are quite out of reach for me at this time.
Maybe one day the shows will start back up. 
I for one canāt wait for this!
Hey @MRHifiReviews, I did the same with my son for years as well. He would listen to an album that I suggested (i.e. Dark Side of the Moon, Brown Dirt Cowboy, Abbey Road, A Night at the Opera, and many more with some 80s classics) and then I would listen to an album he suggested (Kendrick Lamar, Drake, etc.)
It was a great way to spend time together, bond over music and learn from each other. Heās now a hip-hop beat producer (aka Contraband - prodcontraband.com) and I hope our weekly sessions helped his love of music and creativity.
In my opinion, this time could be spent with even an old radio with cassette, the time together is the best part. Now if the music sounds great thatās a bonus.
Just my two cents, for whatever thatās worth.