I’ve had the ABM600, currently got the RM500. For me the gain on the ABM was more like a “thickener” to the sound, making it warmer, chunkier and with more harmonic content, but never overdrive or distortion like.
Whereas the gain on the RM is more (to me) like a distortion pedal, as such I keep it about 9 o’clock to add something in but any more than that I find to be too much, all I’m after is a bit of break-up, any more and it’s getting Lemmy. Might well be the sound you’re after though, from your description above.