I guess that way should be fine, it is the way Toku ended up using his pair in another A300 thread here. I would just caution that I personally would not leave these with volume on full 60 and just use preamp attenuation, not sure these were built to be full on all the time …I've gone back to using them in mono BTL mode, with no BTL connection on the 2nd amp. I don't use the SMSL remote, controlling system gain through my main preamp's remote. But I still find overall amp gain easier to balance and tweak when both amps are separate from each other.
I've also noticed in the short time of using this type of connection that the overall sound is a little clearer and better defined. Not dramatically so, and it may well have to do with the way the amp's gain are presently set, but I find it a bit more resolving and I like it better.