At what distance are balanced XLR cables needed?

There are no guarantees. I have heard of people resorting to balanced cables for much shorter lengths because their situations involve lots of EMI. (Do you live near a radio/TV transmitter?) Recording/mastering studios have miles of cables all influencing each other.

So, my cables are no less antennas than anyone else's but, as far as I can tell, they are not picking up any signals inside my apartment. Literally, YMMV.

Kal

If Zone 2 is really 51 ohms you could use that output. 300 ohms is a bit high for solid state but it will probably be OK.

Bear in mind that you can spend an arm and a leg for unbalanced interconnects made with exotic wire. Balanced interconnects don't need exotic wire, and might cost you less.

Eldartford - you can spend arm and a leg for a balanced IC as well. They're also made of fancy materials - both metals and insulation. There is no reason why it should be different IMHO. Purity of metal still applies since impurity reside between crystals while insulation material directly affects capacitance and dielectric absorption.

The superior connectiviity of a balanced connection makes it an easy choice--if you have that option. And while Kinjanki makes a valid point, reasonably priced XLR cables are widely available. A well-known manufacturer touts Belden cables with decent connectors for his very pricey gear. If it's good enough for him... Kal's comments are certainly valid also. Try borrowing cables from the Cable Co. The only downside is that they probably have limited choices in the lengths discussed. Blue Jeans Cables might be a good, low-cost option for you. Just my $.02 Good luck!

Kijanki.. And you can pay an arm and a leg for little stones.
Atmasphere, whose opinion carries a lot of weight, has suggested that fancy wire is of little value in balanced interconnects.