Smells like BS to me.
Ask him to do a blind A/B test with the 'bass' cable and a normal cable, see which he prefers. I bet he can’t tell the difference.
Reminds me of a story:
A few years back I worked at an audio / video store... we set up a high quality integrated amp, a very sweet set of speakers and 2 identical high end CD players for an A/B test of wires.
We hooked up one CD player to an input of the amp using the cheap RCA cables that came with a low end tape deck. The other CD player was hooked up to a second input using $250 monster cable RCA wires (the kind that even specifies which way the signal is supposed to flow through the cable.)
On a blind A / B test, some people chose the cheapie RCA (including my manager), some chose the high end cables and some could not hear a difference.
After that they never got on my case for not pushing monster cables again

. Maybe in $30,000 systems you can hear a difference, but unless your near perfection already... there are better ways to spend your money.