anomalee, I think bassist15 mentioned the fact that he likes the Led Zep sound on the Led Zepplin II album.
So bassist15, I'll say that Hamstir is pretty doing the same as I do. Try to set it all flat, and then experiment with what you like or not. And the room where you play is surely affecting your sound, so that's what you refer for using the EQ to work for you. Don't forget though that you're trying to push hard on the
ULTRABASS BX1200
120-Watt 2-Channel Bass Combo with DI Out
and I guess that if you use the ULTRABASS subharmonics processor it might overload the 1x12 at high level. So maybe try to deactivate it (or turn the knob counterclock) to hear if you can boost a little on the bass - low mids , and cut a bit of the high mids and the treble of the EQ section.
this is just me trying to help, and sharing my thoughts on the matter.
If you are looking to change for another rig, I could suggest some amps that I think, will give you that round deep solid sound you seem to like. First I think it's the warmth of a tube amp you feel. Such has the Ampeg SVT-CL, all tube head. I think Fender good one too . The SVT-2PRO might also be to consider, maybe better then the CL. Next you could also get a pre/power amp setup. I'd choose the Ampeg SVP-Pro, SVP-CL, the BBE bMax-T (that I will have soon

), Aguilar seems to have a deep sound... but make yourself an idea, because you can hear them all at
http://www.basstasters.com/
anyway, I'm sure that if you search in the many threads of the talkbass's forum, you'll find as much as I am searching in the quest of new rig

, I am discovering, and learnig my way to sound realm of the bass...
like sedan said, if you could hook up other speakers to it from the speaker out 1/4 mono jack connector, that might be a good add. Also you could run an XLR from the DIRECT-OUT connector to the console if you got a PA and other speakers.
I hope this will help you...
good luck
edit: I have forgot about the MESA 400+, Trace V8, all tube heads that are also legends I think...