Since you're talking about the speakers, I feel I should once again voice my very strong recommendation for the
OEMAudio+ speaker kits for the FT86—in particular the
Reference 400CF.
It replaces the factory tweeters in the dash and the 6.5"-ers in the doors, adds a new fitted subwoofer enclosure in the trunk which includes new amps, and bypasses the factory amp and the stock dashboard mids. The new main DSP amp will be specifically programmed for whatever HU you're using (they ask you when you order what HU you plan to use), and they can program the subwoofer at 3 different levels ("balanced", "full", or "robust" IIRC; I picked the middle level, as I like
some thump, but not too much).
A bit pricey, yes, but well worth it if you want a great sound system in your 86.