Hi ajhuntsman;

Sorry it took me a while to get a hold of your question - these Hybridfest trips can take a toll on one's schedule.

The HCH-II is an extremely poor platform to support the kinds of demands and 12V subsystem loads that a powerful audio system will call for.
To put it in the most basic of terms, the design faithfully follows the "minimal optimum" principle or "machine minimum, man maximum" Honda philosophy in that the system has barely any power headroom left for after-market devices unless you are willing to take on an ever decreasing fuel economy or you supplement the missing charge through other means.

If you live in a predominantly moderate climate and the power signature of the device is reasonable you may not have any issues at all.
If you live in a colder climate (winter time) then your 12V battery will undoubtedly have a shorter life and you may end-up experiencing IMA related malfunctions sooner or later.

The battery should be good for the occasional short lived demand of peak current. However, even a non-stop 100-200 mA is enough to bring this battery down in matter of a few weeks so it all depends on whether you operate the equipment with the engine off or not and for how long. Your commute distances also have a bearing. Shorter distances are usually worse.

The charge rate/frequency is managed by the car and the DC-DC gets its power primarily from the battery pack. On a moment's notice the DC-DC inverter can provide all the current you need but not in sustained mode.

I would avoid running more than 100 watts (approx 8 Amps) on a regular basis.

Cheers;

MSantos