Cons of using main XLR/Balanced outs for subwoofer?

Will that configuration really make a big difference?

@rlb61 Did you notice a difference in the mains between not having the sub hooked up and all, and having it connected but its volume turned all the way down? If there is no difference then your RCA output is buffered from the balanced out and the ISO MAX isn't needed. If there is a difference then this is the solution.

Dear @rlb61  : You own very good two-way speakers with a " little " trouble and this is that crossover at 2khz so the woofer runs frequencies from around 35hz to over 2khz and no matters what that facts says that the IMD and THD distortion levels are higher than desired to listen MUSIC.

I know that you are not really happy with your JL sub:

"""   I’ve concluded that a subwoofer is not necessary in every application where a 2 way speaker is used  .. """

by the contrary the conclusion is the other way around: with a two way speaker design subs always are need it.

I know too that your room is not to big but this does not avoid the sub use or integration.

The first premise to add subwoofer to any system is that must be a pair of self powered subwoofers and never only one unit, this is not the way to go. You need a pair of subs and if you follow the information in the link I posted you will be way satisfied with.

Now, adding a pair of subs running in stereo way is not plug and play we need time and patience and if you have it then you will have success.

Your Pulsar will shines as never before and you will have all the frequency ranges at the higher quality level performance you can imagine: really good an accurated bass range handled by dedicated woofers and dedicated amplifiers and the same in the mid/high ranges where your main amps will performs better than ever when are not running low frequencies that diminish its overall quality performance and headroom, now you will have pristine and addictive Pulsar MUSIC sound reproduction. Remember, you need two subs.

As I said in other post: is up to you.

R.

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.