First link on Google for Maxwell bank is one for 280$ on Alibaba. I figured 350 would be about right after shipping if you weren't buying freight quantity, but OK, what's your price on them?
I have some YingLong 40AH cells I'm selling for 50 ea. 75ea is the high side, but compare cycle life to non Titanate flavor LiFePO and you're coming out way ahead in the long term. For what it's worth I don't think anything (especially shipping from China) is getting cheaper going forward so whichever way you go don't wait too long on this.
Quite a spread on the price of Headway cells. At 40 for an 8AH bank they would probably be worth buying at 80 not so much. (83WH/KG energy density on those which puts them about middle of the road for various flavors of LiFePO).
Do what you like, but do understand the actual energy stored in your supercapacitors and plan accordingly. This isn't a matter of "why do you need to get stupid loud", it's more like "why are you buying a 5500/F550 series pickup truck?" If you're looking to tow something big you're choosing the right vehicle, if you're looking to compete in a F1 race, not so much. Either way this **** isn't free so you had best to figure out what your electrical system needs to do, for how long, and manage your space/weight/budget optimally because you don't have unlimited of any of those things.
Lishen also has what 25C rating vs 10C for YingLong? For purpose of burst current the 18 Lishen should outperform the YingLong 40 at the expense of reserve. Personally I'd use 2 banks for what you're doing just to make sure they never operate above half their max C rating but you're certainly using either within their specified limits. What is your experience driving around or parked playing music with either? You have a voltage gauge?