Using Mark Levinson No. 380 preamp output simultaneously

Why would you do this?

Some subwoofers require a line level signal from the preamp. 

I have a Levinson Reference No. 32 preamp (no longer in use, loaned to a friend).  I use to use two outputs--one to the main two-channel amplifiers, the other went to an ambient sound synthesizer that fed four smaller speakers set up to the side and rear of the room.  

That is a less common use than for subwoofers.  Most linestages can accommodate two outputs--whether by having two sets of jacks or use of a splitter--and there should be no problems with significant sonic degradation.

I have a 380s.....I've used both outputs to biamp my Infinity RS-1s for 20 years or so.

You can use it but it is not ideal.  The manual urges against it.  A better solution is to use a splitter off the balanced output and an active balanced to single ended converter.

Thanks for all the help..
@willcycle why is it not ideal? I was actually  thinking  about running the balanced to my mids and highs, and use the rca for my woofers (biamp) since my amp for my woofers only has RCAs