The Pass Labs X0.2 have two pairs of variable XLR and two pairs of variable RCA. All usable at the same time with its single volume control or remote. The Pass X1 and X2.5 have one pair of each type that are variable.
I use my X0.2 with multiple amps and will use it with active crossovers eventually. Works simply and flawlessly.
It should be easy to use the RCA connectors for the Subs on any of the units. Remember that on preamps, the RCA outputs will have a lower output than the XLR, but almost all amplified subs have output controls on them to compensate for this little bit of difference.
Also if you ever run a Theater preamp through it, all three of these have a unity gain pass through for that purpose.
Hope that helps.
Best Regards,