My current setup:
I love the sound of my A4 but I don’t like very much the Bass sounds
I managed to do some good sounds with the OB6 but I want more.
The machine must be:
What yould you suggest?
Moog Minitaur springs to mind immediately
The 0-Coast is an amazing little thing!
Pulse 2.
Dreadbox Erebus
Why can’t you use the OB6 in mono mode. Isn’t that an SEM in mono mode anyways?
The fact that anyone answered is strange to me. How can we give a GOOD answer if you don’t tell us your intentions? What kind of music do you make? What kind of bass sounds do you want? Do you want mainly sub bass or sub bass + mid bass? Do you want snappy/plucky envelopes? Knob per function? Live use, studio use, or both? What is your synthesis skill level? Do you care more about sound quality, workflow, ease of use, footprint?
Given the gear that you’ve already purchased, I get the feeling that you haven’t yet found “the sound” that you’re looking for. I feel like the missing piece in your current setup is something with more character. The three synths you have are all similar in that they are “safe” “all-around” synths. No disrespect intended, they are all great synths, but they are fairly straightforward choices in the current landscape. I’m all for getting some straightforward synths that have a lot of scope and range, but after that I think it’s good to get one or two strange synths with unique character that are hard to miss.
I think we could all list off bass synths for quite some time, but if you want us to list of the ones that will actually suit your needs, we have to be aware of your needs first. 
Another A4 or a AK. The A4 makes GREAT bass. Or even an AR
Ti2 should handle bass pretty well too.
AK/A4 > Analog HEAT
Novation Peak > Pultec EQ
Something with CV input would be ideal, as you’ve got that A4 CV track to use.
Moog Miniatur is nice and gives you CV input to p-lock filter cutoff and volume as well.
It also responds to the MIDI program change that A4 can send. So when you change patterns on A4, it will respond accordingly. And 128 patch memories. So conveniently compatible.
Try out the Korg Monologue.
Moog M32 is my bass specialist, controlling via A4 C.V. is a blast.
agree on the minitaur - has memory and can use your cv track.
I own an A4 and a Minitaur. After two days of trying to get the Minitaur to “pitch” correctly, I gave up. The sound of both together was absolutely perfect but the setup woes were just too much. I want to give it a try again soon but I haven’t been able to find any new info that gives me hope that it will work.
To the OP, the Minitaur is one of the best sounding synths I’ve ever owned and I’ve had a lot of gems, but the very necessary editor is still a little buggy and the CV setup is a PITA (for me at least).
To everyone else, are there any solid guides to get this setup working?
Another vote for the Moog Minitaur. I drive it through the Monomachine.
This.
To everyone else, are there any solid guides to get this setup working?
Tried these?
Wow, that was quick!!! Thanks Rics, I’m gonna dive back in.