I have heard bad things about mralternator. Go to sounddomain.com and termpro.com and search around for HO alternators. In this arena you really do get what you pay for!! If you want the best...go to ohio generators...they are the best alternators out there.
I would try to look up a local alternator shop in your area...they should beable to rewind the stock one to get the proper output. The output at idle is what is most important, not what you get at high RPM's!!! That's where most dimming occurs. Many cheap alternators advertise maximum currnet capabilities and are very poor at idle speeds...the result --- all your money down the tubes.
Make sure you upgrade the under hood wiring as well, nothing less then 4ga.
For 800W, you must have a 500/1 and a 300/4.....both can be current hogs, but shouldn't be too bad....remember under typical listening conditions, you are not going to be using the maximum current draw for your amps....the typical honda alternator is between 50 and 60A....anything that is above 100A with the proper wiring/install should be appropriate.
Have you looked to see what is available in the honda passport? They may come with a stronger alternator from the factory....being that it's OEM, it may be a plug and play style install...just another idea.