At what distance are balanced XLR cables needed?


I've been looking for a new preamp for my 2 channel system, and I'm debating whether I need balanced inputs if I want to eventually connect it to my home theater processor. I plan on moving soon, so I can't say for sure what distance I would have between the two systems. My preamp options quickly dwindle if I require XLR cables.
hoffer71
If the HT Processor output impedance is about 50 ohms or less (typical for solid state) 20 feet should work fine.
Hope this helps:

My HT processor is an Anthem D2V. According to its specs, its input impedance is 20 kΩ, and its output impedance for "main" is 300Ω (RCA), 600 Ω (XLR), and for "zone 2" is 51Ω.

Impossible for me to determine EMI, but I plan on moving to an apartment in Manhattan.
I run 10meter interconnects, balanced and unbalanced, in Manhattan and have no noise problems with either. FWIW.

Kal
Thanks Kal. When discussing the output current, I'm assuming you meant my HT's output. If my apartment is relatively noise free, any concerns with running about 20 feet unbalanced given the d2v's impedance?
Kal, 10 meter unbalanced and no problems? How did you manage that? Unbalanced runs tend to act like an antenna in my experience, I had to resort to long runs of balanced interconnect to mitigate the attenuation.