Just curious, I do not see anything in the forum about the separate amplifier and speaker options that are available.

There is the stock HU-613
It has three amp options: 4x25, 4x50, and 4x75
It has three speaker options: performance, high perf, premium

Then there is the HU-803
It has one option: Audio Max

Who has some knowledge of the differences in specification of the speakers and the amps. There seems to be a question if the 4x75 amp is even available and then a second question about the differences between the speaker packages.

I am interested in what the differences are in the speaker groups. The cone material is likely the driving factor, probably magnet size as well. Seen any specs?

On the amp: power differences are rather clear, but are the THD levels significant?

I know that a couple of you have purchased the upgrade, but what about the options individually. Apparently the HU-613 is very similar in specification as the HU-803, but is four channel limited rather than 4 + center +1 simulated PLII. Otherwise, any major differences?

Any info, prices, experience is appreciated.