Recommendations on Hooking Up Dual Subwoofers and Speakers

Hello,

My new integrated amp that's coming (Technics SU-R1000) only has one unbalanced "pre-out" and one unbalanced "rec-out" and I want to run dual subs. Ideally stereo sub set up, but open to mono subs if necessary.

Could I just run RCA cables from the left channels of both outs to the left sub, and right channels of both outs to the right sub? Or should I just go with a splitter off the back of each of the pre-outs (2:1) and do it that way?

My sub's (KEF Kubes 12b) do have speaker level connections which I currently am using (but just have one sub hooked up now). I'm gonna also integrate my system into a 5.2 set up so speaker level connections would complicate that process with my sub's coming from my AVR... Right, front left and right channels sharing speaker input in a 5.2 setup (problem right)?

Is there any way to run speaker level sub connections AND integrate everything into a 5.2 set up if possible, as opposed to just RCA?

Just wondering what other people have done and recommend?

On a side note, 4 terminal speakers, is bi-wiring worth it, or only bi-amping the speakers? My new amp and speakers come in the next two weeks together (JBL L-100 Classic 75th anniversary).

Thanks