I've found what others have posted on here to be true as well. Sucks as a "distortion" into a clean amp/channel - works excellent as a boost! Now I understand why players like Satriani and Vai had, at one time (and may still?), used them in their rigs. Want 80's hair metal heaven with harmonics galore? Boost a Marshall or slightly dirty amp of choice with a DS-1! This works beautifully, IME.
Also, the Keeley mod IS very bassy (but not a bad thing, IMHO). But I used the Keeley as a boost also, and the tone itself didn't seem too different from a stock DS-1 (the newer ones) other than the boosted bass.
All IME, and as always, YMMV.