Dual Subs set up advice

Run your RCA lines from your preamp as you suggested in option #1.

I"d insert an active x-over in the loop. I use NHT, which is versatile, undetectable (to my ear) in the main path, and relatively inexpensive. This does put another component in the signal path, but (as noted) I find it benign and the seamless hand-off you achieve will be well worth your effort, IME and IMO.

If you really want to see what's possible in this type of set-up, slip an SVS/Audyssey or Velodyne room correcting sub equalizer between the active x-over and the Descents (it will EQ the subs only, and be out of the main path, entirely). I use the Velo SMS-1 (again, relatively inexpensive), but some swear by the SVS unit.

IMO, this was the single biggest audible improvement I have made to my system in the last 20 years.

As always, YMMV, but the SVS, Velo, and NHT units are sold direct with money back in-home terms. If you M does, in fact, V from mine, you can ship it all back at little to no cost.

Marty

I use speaker level in on my RELs.

I run RCA out of a SF Line 3 to the two stand alone amp/crossover units for my two Genesis subs. The Genesis subs can be run solo, not dual, so the amp/crossover unit has L and R RCA in. I use the L on one unit and the R on the other.