Cons of using main XLR/Balanced outs for subwoofer?

two of these op-amps are to buffer the signal to the tape output and level control, the remaining four for the two balanced outputs. These integrated circuits are specified as delivering high output with low noise. "
Could we deduct something from these facts?

@c

Yes. The tape outs and volume control have nothing to do with this. From the statement I would also deduce that the RCAs are in parallel with the balanced outputs, so if you load both even though the preamp is perfectly capable of driving the load, you will probably notice an artifact and more noise could easily be it.

@cardani  : 5 subs, so your Vandersteen and your main amp are really happy hadling the mid/high frequency ranges, good.

If you can connect a decent amplifier maybe coming from one of your friends instead the Dayton and se what happens.

Bryston know perfectly its products and I insist that contact them directly along that other amp tests..

R.

Thanks Ralph @atmasphere , so it seems like there is a good chance for improvement since you said before ¨If the RCA outputs are in parallel with the balanced outputs on your preamp then what you describe makes sense. If it were me I'd be using the Jensen ISO MAX¨
   I will check it out, Thanks a lot!

@rauliruegas
"If you can connect a decent amplifier maybe coming from one of your friends instead the Dayton and se what happens.¨
The think with the Dayton is that it is also a sub x over preamp, but i will check out if its possible to bypass it amp section (1000 w class AB) and yes borrow another Bryston or something good to try. Yes 5 subs , two Vandersteen 2wq with their highpass filters at 80 hz and 3 passive B&W,s that are moved by the dayton 1000 sub amp. The mains are the Gradient Revolution, and yes very easy load for them with the help of the subs.
Yes , i will contact Bryston and see what they have to say.
Saludos Raul!

@atmasphere

Ralph said "So if you have a balanced output on the preamp and a single-ended input for the sub, the ISO-MAX Jensen box is the elegant solution". 

Question/clarification...since the ISO-Max transformer has a single ended input and a single ended output, are you using something like this Neutrik adapter to go from preamp balanced out to transformer rca input?

Neutrik NA2FPMM 3 Pin XLR Female to RCA Plug Adapter (parts-express.com)