I considered using a balanced cable from the DAC to the preamp. There is a note in the Okto 8 Stereo DAC manual about this (quote below):
"We highly recommend using balanced cabling between analog audio components whenever possible. The main reason is that, due to the different reference, ground is not a part of the balanced signal path. This makes equalizing currents created by ground loops and electromagnetic interference, which would otherwise be injected into the signal, harmless. If you need to interface the dac8 with a legacy pre-amplifier or a power amplifier that has single-ended inputs only, there are three methods to do so:
1) A solid-state conversion circuit, for example the Neurochrome Universal Buffer
2) Audio transformers like Lundahl LL1584-3FXPHM
3) A special adapter cable with floating pin 3, like “Benchmark XLRF to RCA cable for analog audio with pin 3 floating”. The cable does not perform actual signal conversion; instead, it only uses one half of the balanced output from the dac8 without shorting the other half to ground. This method will result in a loss of performance, but it is recommended as a cost-effective way to connect subwoofers.
Warning: We strongly discourage the use of balanced-to-unbalanced cables and converters. Doing so will result in significantly decreased analog performance due to the short they present to the output of the dac8 Stereo's analog stage, potentially overloading it and risking damage after long-term use with high signal levels. Warranty does not apply to units with analog circuitry damaged by using XLR to RCA cables and converters."
Methods 1 and 2 are both quite costly.
Your solution is like their method 3; it suggests a loss in performance. Not sure how much. Their warning note scares me. Running 25 ft. of unbalanced cable, better or worse?