At what distance are balanced XLR cables needed?

Atmasphere... So the 100 ohm output, balanced, from my Behringer DEQ2496 is OK. Whew!!

Your preamps are no doubt better than the average tube gear. 600 ohms is what I always saw with the mid fi stuff I used.

Output impedance is not that important within certain limits. My Benchmark DAC1 has output impedance values from 60 to 1600ohm dependent on output divider jumper position. Benchmark recommends for 1600ohm output maximum cable length of 26ft - assuming typical 32pF/ft and 0.1dB drop at 20kHz. With my cable (6pF/ft) I could go 139ft.

Kijanki, with the 1600 ohm parameter selected, it assumes a high impedance at the other end as there would be distortion if it were actually driving a load of a lower impedance.

You will hear big differences in cables with it set up this way.

As a general rule of thumb, the output impedance should be about 1/10th of whatever it is driving. So the 60 ohm position *should* be able to drive a 600 ohm load just fine. And FWIW, many solid state preamps can do that. Its the tube units where this is a challenge.

So if you set the unit to 60 ohms and then place a 600 ohm resistor between pins 2 and 3 at the input of the amplifier, the result is that you will not be able to hear differences between interconnects, regardless of cost.

I have a McIntosh C2300 preamp feeding a McIntosh MC402. They are 16 feet apart. I have used both Balanced XLR connections and RCA single ended connections. The balanced has sounded better every time. By the way the RCA Single ended cables were supposed to be more highly regarded and definitely way more expensive.

So, to answer your question, I found 16 feet the distance in my system.

I would suggest using the very best cable and connectors available, and if that means using XLR's, by all means use them.

Atmasphere, unfortunately I don't like gain at 60ohm position. Not many solid state amps have 60ohm output impedance while the most of them cannot drive 600ohm. The reason for that are op-amps used. Only few like LM4562 or OPA1611/12 are designed specifically for that. In addition most of preamps have output capacitor not designed for 600ohm load. I used to solder resistors left and right when I was young. Now I know better and do always whatever is "standard".