I’ve been using the cross feed function embedded in the firmware of the Topping D900 for about two weeks now. The results when selecting convolution and studio are excellent. Once you listen to it fora while, it’s hard to go back to no cross feed. The function in the D900 is pretty advanced compared to most available options out there.
What I’m noticing is that the headphones present a completely different sonic character with cross feed as opposed to not using cross feed. This cross feed function does simulate listening to speakers pretty well (IMHO). I’m also finding that the EQ values do not work the same when the cross feed is applied. Generally, the need to EQ seems to be reduced (subjectively) by a fair amount once cross feed is applied.
The PGGB developer is working on their version of cross feed. No ETA yet, but stay tuned.