Cons of using main XLR/Balanced outs for subwoofer?

Thanks @atmasphere and @rauliruegas for the advice. It in not that I get hum, is just that with the dayton sub amp I get minimal white noise at around 120 hz and what i think is a higher noise floor. My bryston preamp only has one balanced and one rca outs, and i use the balanced ones first a Vandersteen m5hp high pass filters which cut at 80 hz and then to my bryston amp , susequently a cable that goes from the amp outputs to to the  two Vandersteen 2wq subs. The unbalanced output of the preamp goes directly to the Dayton sub amp and then to three 10 inch B&W passive subs.  So yes , a total of five subs.
Ralph, I will try the advice you gave to @rlb61 as i think we have a very similar case. I just want to make sure that by adding the use of the unbalanced  pre outputs to Dayton i am not degrading the signal in any way as pointed above ¨Unless the preamp has entirely separate circuitry driving the RCA and XLR outputs, when driving both you will have a lower impedance load on one of the XLR signal pins (pin 2 or 3) than you do on the other. The preamp may make less voltage on the pin that has the lower impedance load, but at any rate the total impedance to ground will be lower on that side even if the output voltage is unaffected.
This will in turn reduce the Common Mode Rejection Ratio (CMRR) that is available to the main amplifier, which will raise the noise floor and possibly also the distortion¨. ´on the other hand @rauliruegas picked up some info from Bryston ¨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? Thanks in advance for your help.

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!