Dont put in a clarion EQ, you will just compromise the signal. Keep the signal line minimal, Higher pre-out voltages wont net you any sound quality or loudness at all if your head unit already does a 4 volt pre-out. The clarion EQ also doesnt help the sound at all, causes far more sound issues than it solves. Cuts all frequencies, doesn't target the frequency you want but kills off the details because it affects the frequencies around it too much. The head unit EQ is WAAAAAY superior than that clarion garbage.
This head unit blows everything you've mentioned out of the water audiofeatures and SQ wise, 13 band EQ, 24 bit dac, time alignment, 4 volt pre-out, NETWORK mode. clarion only has a 5 band EQ, ewww. I've tried both the clarion and this head unit and this head unit outright sh*ts on the clarion. That alpine you listed is junk with zero audio tuning features. those particular clarion and alpine models are both outright horrible buys compared to today's head unit standards.
https://www.crutchfield.com/S-aiOkx8pxtQg/p_105KDX340B/JVC-KD-X340BTS.html
PS this is not JVC's unit its actually kenwood based so expect kenwood quality.