admittedly, i was confused there a bit too. splitters or ‘Y’ cables introduce another segment of signal loss usually less than 3db, but loss of 1 or 2 for sure.
then too therre is the introduction of differing cable materials and in this case connectors and or splitters are different ICs essentially.
eliminating signal loss is always a very good idea. albeit, one will figure the gain of a pre or line stage, and or an amp will forgoe this loss in connectivity, I’d avoid it if possible.
I might be picking nits here and one or two db of signal loss at one sub might be undetectable . dunno.
it will help keep the signal path more secure though and likely prevent the coupler from getting unplugged inadvertantly.
as this is for the lowest octave chances are there won’t be any overtly audible discrepncies.
+1 on using the ‘left’ input on each sub regardless the output on the pre, ‘L or R’.
i would say get the sub info from as far down the signal chain as is possible, i.e. the pre in your case simply for timing sake. ten ft ain’t a lot of conductor so the 22ft run ought not show up sonically as a deleterious issue.
good luck.