Yeah, going for old good amps could be very sane and often brings something nice to the table. No doubt! However, I am always wary of such products regarding generalized discussion.
Typically old amps use less negative feedback and less active dc servo circuits. This per se is desirable in my opinion. The problem is that such circuits assume internal parts remain good. I know some followers of a legendary Japanese amp like Panasonic M-22. And I’ve also seen some of them needed to be overhauled or repaired to get things right. Not sure about Sansui or Marantz but I am suspecting product-to-product aging variation to the same extent.
If I go for SR1a, I am not willing to spend that much money. Can’t afford it. 
Schiit’s power amps seem more plausible ways – but not sure about how they paired with SR1a. In this regard, @pavi’s report is encouraging and @torq’s (comparative) review can help me too. Nevertheless, reading SR1a threads in various places, it is just a realty that a median SR1a user spends at least $3k-ish (new) in their power amps to drive this headphone.
Off-topic, if Aegir x2 could drive sr1a, then I am hoping Vidar (stereo) could do the same thing voltage and current-wise. 