Subwoofer Options With No Spare Preout

I only have one preout on my preamp, and I’d like to add a pair of subs to my system. I’m curious peoples thoughts on the best method. I have a few options in mind that I’d like feedback on but if I’m missing an option let me know.  First option I’m considering is a pair or Rel’s which would be pretty straightforward to setup. I’ve also thought about getting a separate crossover with both high and low pass filters. I know in theory this is likely the best solution. I won’t be working with a large budget so something like a Sublime Acoustic K231 is probably the best I could manage. The likes of JL audio, Bryston, and Marchand are bit out of budget.  This would allow me to use any subs I’d like, possibly even some DIY passives. The last option I’m considering is simply splitting the one preout and running one channel to each sub. I know it’s not ideal but I do have considerable excess gain in my setup even though my pre only has 9db. I never get past 10 o’clock but generally at high volume I’m around 9 o’clock. 
 

My system right now consists of Audio Mirror Reflection monoblocks, a Canary C630 pre, Totem Arros, and a Bluesound Node.  The room is 9ft by 11ft with 8 foot ceilings. I’m still uncertain if my next purchase will be subs or a new digital front end. Both will happen before to long because I need more bass and I know the Node is holding back my system considerably.  Anyways any thoughts or opinions are much appreciated.