I have both the EZQ (currently sitting in a box in my basement somewhere) and the ACG pre. I like the ACG a lot better. It's in my Starfire and it's the closest I've heard to the Alembic modified Starfires. My ACG is an early one, so it's got separate filters for each pre. It's dead quiet and very versatile. I like it better in some ways than my Series I electronics because the filters goes all the way down to 70hz, for some very cool deep tones. I wish the filters went higher, though. They only go to 3khz and there's high frequency control to take up the slack, but it doesn't go low enough. It would be perfect if you could overlap the filters and add the straight tone to the filtered tone (sound familiar?).
I have a SF2 as well, which gets a lot of use, although since I started playing through a SMS Classic preamp as a front end, I've discovered that onboard tonal changes come through a lot better.
The EZQ hasn't been in a bass for a long time. I suppose I should fire it up again and see what I think. The bass boost is a good aspect to it. It's nice to tune in the high or midrange frequency you want and then be able to kick in the low end.
I also have an early Rick Turner onboard preamp. It's got some very cool tones. Again, it's sitting in a box somewhere, but I remember it being a fun preamp to use. I guess I should put these guys to use!
Edwin