Well, if already installed, then try to tune it to sound nice.... Twweter placement are something you can adjust.... Facing towards you, facing towards rear view mirror will create different effects on your system....
JVC HUs are quite decent, unless you get those unknown China brands....
Unless your money comes easily, then you can just change whenever those acc shop operators says so....

The midbass you can't do much, only the tweeter can.... You can do like that(fiberglass), but not worth....
The "good" sound is explore by you, not me... But that's the 2 placement you can try along....

Just to add, what ever money that being used, leave it, don't change anymore.... If not, you will end up waste more money....

If the amp was designed for that sort of connection, then it'll work fine la. Why you worried about heating up?

Be very careful not to bridge or hook up the amp to a unsupported impedance (eg - hooking up a 1ohm sub to a amp that only supports 4ohm bridge). This will heat up the amp super fast and probably cut very often. Eventually too much of cutting and you can say byebye to the amp.

If you hook it up 400W @ 4ohm bridged to a sub that's running 4ohm, then you're meeting the amp requirements to run properly. If that amp burns out and spoils easily just because you bridge it and it gets hot, then I suggest you change the amp to something else better. Amps if specified to do something should do exactly that thing without problems. Assuming you bought a reputable brand, it will be fine la

Hifonics is a reputable brand la. Soundstream also ok. Between the two I dunno which is better because I never used either one before.

Love so much HCCA 250/275/2100 G4 & G5 edition.......

- distortions and noise could mean many things in audio world and the term itself is also very subjective

- sound proof doesnt solve sound waves bouncing around your car cabin

- dont have to *blast* your sound system to experience distortions or noise. the only difference between blasting and not is the higher your volume goes, the easier and noticeable flaws (distortion/noise and/or more etc etc) on your sound system are

sound re-production is not a a then b thing, all the drivers have to work together in harmony to produce accurate (and "insert positive audiophile term here") sounds. if you would like to know more, i would suggest google/wiki on "sound reproduction" or "speakers" with relevant sources/references/links/"see also" from them

I'm driving 1st gen harrier, recently install with focal access 165a1, focal solid 4 and woofer focal 25a1.
My installer just place my tweeter at stock tweeter position, and speaker at front door original position. Just wondering the position is ok? And my power cable to amp is around 8m, rca cable around 5m. Just wonder there is any sound downgrade issue or not.  The installer just installed everything then got sound done. No position tweeter location one. Amp gain i set myself. The boss adjust the setting on HU only.
And using Pioneer Deh-6350sd HU.
Audio quart  5m  RM210 each. Duno how good the cable, the best can be found in shop..
other cable cost me around RM520, audio quart brand..

What is the next recommend upgrade? Sound proof the front door? Or buy a monoblock?

we share the same feeling bro   

only use one, switch amp one off, use hu one.. nothing bad will happen, but u will be getting 80hz not 100hz from the sub