If you are going used, you should easily be able to score a pair of PS Audio XStream Reference Bi-wires. 8' pairs typically show up for $300-500/pair. This is a cable that was purpose-built to be bi-wire. The bass run uses huge solid core copper conductors in a few different gauges; the treble run uses smaller gauges of silver-plated solid core copper. The very low impedance of such a huge speaker cable (about 2 lbs. per foot) should serve your low-powered amp--and especially a tube amp's higher output impedance--well.
If the set you score is fully intact, it will include interchangeable screw-on spades and bananas. I don't know what kind of speaker terminals your amp has, so maybe the bananas would be better. One caution: These are huge and heavy speaker cables, so you may need to get two or more C-clamps to anchor the cables to the amp shelf so the weight of the cable doesn't snap off the bananas or drag your amp or speaker off its shelf or stand. I use a C-clamp to ensure that mine doesn't pull the center channel speaker off its shelf above the TV.
Still, electrically and sonically speaking, for fullness, weight, speed, and transparency, these are a good candidate. They were originally $1500 cables and look, feel, and sound like it.
If the set you score is fully intact, it will include interchangeable screw-on spades and bananas. I don't know what kind of speaker terminals your amp has, so maybe the bananas would be better. One caution: These are huge and heavy speaker cables, so you may need to get two or more C-clamps to anchor the cables to the amp shelf so the weight of the cable doesn't snap off the bananas or drag your amp or speaker off its shelf or stand. I use a C-clamp to ensure that mine doesn't pull the center channel speaker off its shelf above the TV.
Still, electrically and sonically speaking, for fullness, weight, speed, and transparency, these are a good candidate. They were originally $1500 cables and look, feel, and sound like it.