Hi all:
I have two systems setup almost the same way in an Acura Integra and a
Toyota 4runner. Both have Boston Pros for the front, and cheap Bostons for
rear fill. Each has a Boston Pro 12" sub in a sealed enclosure and both
are
driven by an Xtant 603X each. There are two main differences between the
systems. One has an older Alpine 7840 (Integra) HU and the other has a
newer
Alpine 9815 (4runner) HU. Taking into consideration the size difference
between the cars it seems that the older Alpine performs a lot better than
the newer one quality wise. The highs are crisper and the bass has more
definition. The 9815 sounds a bit dull. I have even tried to change the
settings with that file you configure and download from the Alpine site.
Has
anyone experienced this? Why could be the reason for the difference?

You can't cross-compare between cars. There is no difference in sound
between the two units.