Impedance matching/balanced connection

Would I be correct in assuming that the balanced output impedance  at 20hz would be double that figure?

Its two outputs, each having that 1.3K value at 20Hz. I've not found input impedance info on your amp, but if its less than 13KOhms single-ended, it could be a problem.

@atmasphere 

Thanks for the heads up regarding capacitor-coupled output. Helped me refine my results using the search function here. I probably should have mentioned my specific gear in my first post. ARC LS25 mkii & Legacy Audio High Current Amplifier (rebranded CODA Stage 3).

I was able to turn up this quote from @almarg 

I took a look at the schematic for the LS25 MkII at arcdb.ws, and based on some quick calculations it appears that its unbalanced output impedance at 20 Hz is in the vicinity of 1.3K or so.

Would I be correct in assuming that the balanced output impedance  at 20hz would be double that figure? If so, that seems a little higher than ideal…

From a strictly mathematical point of view you should have no problems. The only gotcha I can think of off hand is most tube preamps employ an output coupling capacitor (ours are direct-coupled to get around this problem) and so the capacitor can cause the output impedance to be considerably higher at 20Hz (often the output impedance is measured at 1KHz, which really doesn't tell the whole story).

In simpler terms, I would certainly try it!