Do high level sub inputs really sound better?

Huh? Low level XLR cables are fine even for long runs.

I have always preferred the high level myself. I am currently using a couple REL subs, and that is what they recommend. You are getting the exact same signal at the exact same time as your speakers. Now if you are using this in a HT set up, I would go with the low level. Get yourself some cheap speaker wire and give it a try. Then if you like it, step up to some nicer cables.

You could give it a try but my experience says you'll go back to ICs.

Another vote for low level.

Some sub users (particularly REL) claim high-level inputs more effectively blend the bass tonality of the main amp with the sub. I prefer low-level inputs, valuing tighter control of LF I'm seeing from improvements in my preamp. But the crossover point is set low in my system and YMMV.