What I do is run both on my Sr. but disconnect the RCA’s which feed my Koss ESP/95X’s Exciter Box whennot in use. When in use, I turn off my M700’s which are XLR fed.
In the future, I plan on getting the STAX Tube Hybrid Amp which is XLR. I’ll simply build a switch box instead of using Y Adapters and risking have two live audio inputs into one.
Poor Man’s Preamp since both the DS Sr. and the STAX boxes have their own precision Volume controls.
As Ted and Paul have mentioned in the past. Running both XLR and RCA in parallel is not a good idea but I don’t believe you could do any long term damage ((check with PS Audio Tech Support - I’ve blown up a lot of non PS Audio crap in the past). If you need to connect them in Parallel, check with PSA first.
I have successfully used these with OPA 627 Op-Amps on Brown Dog Adapter Boards. and replaced the cheesy off brand capacitors and have had excellent success.