Don't swap, daisy chain them together using the variable controlled Sunfire as the master using the low level RCA outputs on your preamp.
A crawl test is worth the effort. Inexpensive custom length cables from Blue Jeans or Monoprice.
Straight up comparison REL T7 subwoofer vs Sunfire SDS 12 woofer. Preferences or opinions?
I already own the Sunfire. I've got a solid bargain on the REL T7 and have verified it works fine.
The other gear is a B&K Pro-10 Sonata preamp, a matching B&K ST 202+ Sonata amplifier, OPPO BDP-105 Blu-ray player for source material and Monitor Audio Silver RX8 speakers. Room is 20x20x13. Is swapping my Sunfire out for the REL really going to make that much difference?
Thanks!
j