The Act 3, unfortunately, stock, ISN'T a dead quite unit, no. It is a tad noisy, but not as noisy as others. It's got about a 90db signal to noise. Others I've had are around 96 or higher...which is better.
I've never had a problem at all with the Act 3's I've owned, and would continue to use them in a pinch for cheaper, quality/superb sounding 5.1 pre's. I wouldn't however own ANY LEXICON! I've sold em over the years, heard em in many many systems, and they're very "plain vanilla" digital sounding pre's IMO. Not so musical, a bit sterile, and I definitely wouldn't use em in a high end 2 channel system on their own, that's for certain! Again, this is my experience.
If you simply want "wiz-bang" surround stearing and processing, and overall quality of sound isn't so critical, the Lex is good. If you need more refined sound, even the old ACT 3 punishes the sound quality of the Lexicon stuff! I say this from years of experience with both brands.
I have an ACT 3 that was moded by the factory however, that's extrememly quite, if almost dead quite from the speakers! It's upgraded to 24/192 dac's and such, 7.1 channel pass through, direct analog in's for all inputs, bass managment, DPLII (at least as good as Logic 7 on Lex). But then something like that's a bit more money used.
However, if you need dead quiet, you'r leaning more towards the Lexicon between that and the standard stock Act 3. Personally, I'd look elsewere
