The problem with SACD is the provenance of the original recording; if the master is DSD (rare) then stick with the DSD master; but it's more likely to be DXD (352k PCM) or some other PCM, in which case stick to PCM. If you want a quick way to finding out which is best, just listen to the depth reproduction.
Yes agreed on batteries and optical! My struggle is to make it such that mains powered USB connected is the same as optical and battery - and I am indeed getting there.
As to modifying my designs - well I am not going to pretend that each is perfect and incapable of improvement; that hubris would lead to my nemesis.
But - this year I enter my 33rd year of designing DACs - I am getting on for 100,000 hours of design time now. But I am still learning things; one project I am working on has taken a couple of years, and I am on the 4th PCB revision - and yet I am still finding subtle ways of improving performance, and discovering new things. Another project - I spent months on some coding, trying to get a particular performance level - and yes in designing gear extra-ordinary small levels of aberrations are audible - but this level I was working on nobody would hear or measure the difference - but it wasn't quite right. Fortunately, I cracked the issue and got the performance I was looking for. But I kept telling myself why? Nobody would ever know - and it was costing time and delaying other projects - but the issue was I would know and I needed it to be right.
So in modifying gear you are more likely to upset something that has been optimised than give a real improvement.