Those are all good points and I've been struggling to make this arrangement work. This is my first studio and the space is determined by the existing room size. The speakers are what I already have and my budget is running out so I need to figure out the sub configuration. The room these are in is 30x13 with a 12' ceiling so I know the 835s are way big for this space. Some 8" would be big enough. But they're what I have and budget wise, it's going to be too expensive and space-consuming to stack 3 boxes or buy 4 subwoofers to point 2 of them back (or 6 subs for that matter) so I'm looking for a cardioid subwoofer solution that I can mount each speaker on. I'll keep the power way down on these and at least I have an excellent setup for monitor speakers. So, as we all are aware, space in this room is going to be a key issue and the speakers I have aren't ideal. A a musician who has never had a studio before, there are a lot of questions that I've never come across so c'est la vie--I'm asking the expert community for help! So far, the QSC 212c is the top contender option that I can find for a 1-to-1 speaker-to-subwoofer pole mount configuration. I'd put the QSC 212s on their sides for better stability/safety, but I'm also wondering, if they'll reasonably handle a pole mount from 100lb monster speakers. And it's not like these speakers are easy to put on a pole anyway, so I'm considering building platforms for the JBLs. Anyway, I can get two (2) 212s for roughly $3.2K and keep the volume way down. I'm wondering if they will work will with the SRX835s. I'm wondering if they will keep up well with the SRX835s or if I should just bite the bullet and grab some JBL non-cardioids. Also, since everything is so large already, I want to maximize the use of space and I'm not a fan of speaker stands.
Re: "having more "regular" boxes that can be configured how you see fit is more flexible from a system standpoint." This is something I've considered. What would you go with in this situation? Is there a good option that would cost about the same as 2 QSC 212c's ~($3200). That's already stretching my max budget for subwoofers. What subs would be best for this situation? And do I need subwoofers at all or will that be certain overkill in a space this size? Since the speakers are 3-way with bass reflex, should I forgo the subwoofers altogether and just rent for outside shows?
Your last point is really good as well: will cardioid do anything at all in a space that size? Or am I on a wild goose chase and I should just get a single omni-directional sub and call it a day? I'd rather have one great sub than two cheap ones and potentially add another one later, but it may be a better option. Thanks for your advice!