P262/p422 noise and gain

1. Both amps show 18 microvolts (uV) as the (white) noise floor.
   Is this solely from the output stage? and totally independent of the input gain?
2. Are the stereo amps able to be ordered with lower input gain on one side than the other… e.g. for bi-amping?

Or would than not be advisable when bi-amping, to help with a bit lower tweeter noise and power?
(Thinking of a 262 at each speaker servicing the HF/LF)

I suppose the other way would be a 422 doing woofer duties and 262 doing HF work… or a pair of 262s.
??