I've used my Headway EDB-2 HE into the the LWA-500 quite often. The EQ isn't completely flat. I measured once, and iirc, there was ~5db bump around 80-100 hz and then a steep roll off below that (I think it was 18db/octave). It's neutral in the mids and highs. That's not a bad EQ curve for bass IMO, but it does accentuate the thumpiness of the already very thumpy Realist pickups (I use a Lifeline). I have also used the effects loop, which seemed to need a little more gain then my Headway has, but the FX loop on the 1000 is probably different since I believe it is in series (the 500 has a parallel FX loop).
I now prefer to use a Jay Ganz Straight Ahead power amp with the Headway. Using the Headway into an FX loop is nice, though, because it has the extra benefit of leaving the front end open for bass guitar for those of us who double, effectively creating a three channel rig.