The thing about the ATTY (and all passive devices) is they can be transparent and they can be colored, it all depends on how long and how good your cables are, what load (impedence) your amp wants to see, and what level you're running the pot at.
Well designed, modern amps may do fine being fed by a passive attenuator that puts out, say, a 10k load. BUT, the problem that I and Brad (who did the schematic for the Main Gain and Function Junction) and other designers have come across time and again is that a great many modern devices are not actually well designed in all the ways they could be. I won't speculate on why this is because it doesn't matter... what mattered was that our device work with them all, flawlessly, regardless of their shortcomings.
As such, what we found was that passive attenuation, while inexpensive and straightforward, as often as not suffered from frequency response and noise issues when used with a good deal of gear that people use everyday.
Even though it runs counter to common sense: in my experience, a no-compromise active circuit made with top quality components throughout will outperform a passive one when it comes to fidelity and lack of distortions. There's a reason the Avocet, Dangerous, Grace, and other boxes are active and expensive: they are squeaky clean and that purity can be relied on no matter what you're hooking them up to.