Any issues to be aware of if driving SET from a balanced source?

Balanced means that both sides are amplified. The middle pin could be at ground or something else.  There are chips specifically designed to combine the balanced signal back into a single signal.  

In short no it won't work.  Single Ended Triode ground side must be ground.  You will need a device to convert the balanced to single ended not just a cable 

Horacio (Lewinskih01), this can certainly be made to work by means of an adapter cable, although you might obtain better results by using a Jensen transformer to convert the balanced signal pair to an unbalanced signal.

See the following link:

http://www.rane.com/note110.html

For an XLR to RCA cable you would construct a cable corresponding to either configuration 4 or configuration 6 shown in the lower part of the page at that link. Use configuration 6 if **and only if** the DAC’s output is either transformer coupled or "cross coupled," and configuration 4 otherwise. What is meant by a "cross coupled" output is illustrated in Figure 5 at the following link:

http://www.rane.com/note124.html

For a TRS to RCA cable you would construct a cable corresponding to either configuration 10 or configuration 12 shown in the lower part of the page at the first link. Use configuration 12 if **and only if** the DAC’s output is either transformer coupled or "cross coupled," and configuration 10 otherwise.

Best regards,
-- Al

This assumes that the balanced system is referenced to ground and not 2.5v.

if it is referenced to 2.5v, any D.C. offset will affect the bias of the amp making it very unhappy. 

Without knowing how the DAC and the amp is wired it is hard to say what is needed to convert the balanced signal to single ended.  That amp runs at a couple hundred volts making it capable of blowing up parts it you get it wrong.

Another factor is what speaker are you trying to drive?  A set 45 only puts out 1.5 to 2 watts

Just use these on the output of whatever is driving the SET and use RCA interconnects.

http://www.jaycar.com.au/productView.asp?ID=PA3800

http://www.jaycar.com.au/productView.asp?ID=PA3802

Cheers George