Question about running bass (pair of subs crossed over below 80 Hz) stereo or mono in Tri-Amped system:

[EJ3]

The system sources are two TT's (Dual 1229 wt SHURE V15 V cart; TECHNICS SL-M3 wt SHURE V15 V-P OR SHURE 300 carts (all with NOS styli [can put new JICO styli on, also]); as well as a better quality KENWOOD cassette deck & an AKAI RTR.
I have now added a slightly modified oppo 205 (will play any DVD region) as an additional source [with some future digital sources planned].
The Pre-Amps are a pair of differently modded APT/HOLMAN's running a 'triplet' set of resto-modded NAD 2200's to a pair of DAHLQUIST M-905's (updated xovers, about 6 Ohms actual [one NAD 2200 bridged mono to each]) & a pair of 12' modded dual 4 ohm voice coiled subs (operating as 8 ohms each) for NAD 2200 #3. LP records generally blend the bass into mono somewhere at or below 140 Hz. Because I am starting to add some digital to the system now (with a possibility that some source material will have stereo bass down to 18, 15, 10 Hz, don't know?), should I run the subs as a stereo pair or mono like I have in the past? Should I switch to one NAD 2200 running the pair of 905's as a stereo unit & run one NAD 2200 bridged mono on each sub? Or some other configuration? (one that does not include adding a 4th amp at this time). Thank You for Your Consideration.

 

[EJ3]

I have decided, based on information from a former recording engineer that I know: to run A bridged mono NAD 2200 for the Left main speaker and A bridged Mono NAD 2200 for the right main speaker (Dahlquist M-905's [nominally 6 ohms] ) and A stereo NAD 2200 for the pair of 4 OHM subs (which are only fed below 80 Hz). When fed a 20 Hz (+-5 Hz) test signal I can hear the subs. So, I think that I am good with this question.