Cons of using main XLR/Balanced outs for subwoofer?

I'd use the Jensen transformers if I were you.
The problem you can run into is that of ground loops when interfacing single-ended and balanced equipment. The transformers sort that out by providing ground isolation. They won't rob you of any impact as they go down to nearly 1 Hz.

2 followup questions to your helpful response. The straight Rowland to Revel connection would be balanced. Are you thinking the balanced to single-ended interface inside the Revel might not provide ground isolation like the transformer so hum could show up downstream in the daisy chain? Second, any significance to fact my Jensen PC-2XR is rated flat to 10Hz vs the flat to 1Hz of the SUB-1RR?
Thanks 

I am now way beyond my knowledge base and hearing the voice of common sense confusion- which could be just confusion, nothing more. You indicate that transformer roll-off will cause phase-shift up to about 100Hz and this is important to avoid. The frequency response of the Rowland's outputs is 5Hz-70kHz -3dB @ 8 ohms, so seems appropriate to output into the Jensen transformer (the SUB-1RR) with flatter F-R response. But immediately downstream from that transformer could be either a Dayton SA1000 amp which doesn't appear to have flat rating below 18 Hz ( its specs are hard for me to understand) or the first sub in a DBA chain (unlikely to have flat rating to less than 20 Hz for my system). Furthermore, setting up a "swarm" DBA usually involves intentionally producing a mix of different arrival times from the subs by adjusting position, phase, polarity, closing ports, etc. Duke always says the ear is very forgiving of small timing errors in the low frequencies such that the speakers + room = a minimum phase system. So I am unclear how a phase shift in the low (< 20Hz) bass is consequential. OTOH he also notes that the ear has exaggerated sensitivity to frequency response errors (non-flat curve below 20Hz) in the bass region, so maybe that is what you are trying to tell me. FWIW, Rowland recommended the 2 channel Jensen transformer for running subs off the balanced outputs in my Concerto (but that was 14 years ago). I again want to say I will be running my Salk mains (+/-3dB at 33 Hz) full range, no high pass crossover. I appreciate your efforts to understand my options.

Duke always says the ear is very forgiving of small timing errors in the low frequencies such that the speakers + room = a minimum phase system. So I am unclear how a phase shift in the low (< 20Hz) bass is consequential. OTOH he also notes that the ear has exaggerated sensitivity to frequency response errors (non-flat curve below 20Hz) in the bass region, so maybe that is what you are trying to tell me.

Duke is right; phase shift is different from delay, and 'yes' in that order :)