Hiss at addition in system LAMM L2

The pre will hiss no matter what you do. The hiss comes from the mosfets in the circuit and higher gain amps on more sensitive speakers will hiss more than others.
You either live with it or sell it. For me, I chose to go a lower gain amp and it remedied the problem well enough for me.

I had BAT Rex in my system recently, paired with BAT 75-SE, and it was "dead silent"- I could only hear very low level ground loop- type cycling humm with my ear literally 1" from the tweeter, which I'm positive, was related to my power lines, rather then Pre/Amp themselves.
So, I guess hiss is a byproduct of less, then perfect design, and not inherent to tubes or mosfets for that matter.

Just for reference, I had the lamm pre in a system with Coincident Total Victory, Revel Studio and Verity Parsifal. There was some degree of small hissing with all but none really annoying except one combo: Coincicent TV with Antique Sound Labs 1009 60 watt monos. The hiss was very audible.
I had a 200 watt Edge NL 10 in that system that was fairly silent, surprising considering the power difference.
Currently the Lamm M1.1 are paired with the Verity and the hiss is only audible if you put your ear to the tweeter.
So in my experience it appears to be a amp gain speaker sensitivity issue.
The lamm pre is the longest surviving component in my system and is the last one that will leave.