Very often, the "hiss" comes from the source, at my place bc I often use saturation or overdriven signals, that is where I use enveloped VCA just before the mixer's inputs
-- -ADR-
Which is pretty much standard op procedure for performance mixer that have no VCAs over level, such as the MixBX, Cosmix, etc. This is one reason that I've been jazzed about Toppobrillo's MiniMix, because you can use some other VCA module as a "pre-level" going into the mixer ins, and then you also get the convenience of its two VCA panners. You just have to keep in mind that audio signals are best dealt with via exponential VCAs, as those are better at mimicking how acoustic devices decay. Of course, if you front-end this with linear VCAs, you can (if possible) use an exponential envelope generator to make those behave like they need to for audio.