newbie here on car sound system , any recommendation to add some good sets with 2k budget and below?? for my hilux truck

Can anyone tell me if it is ok to connect both High level and Low level input of the amp? My car 1st Gen Harrier stock HU (6cd changer and navigation cd receiver)only can do High level output i think. And i would like to add a new HU for USB support. Since new HU with RCA output, i'm thinking to connect to the RCA of amp, and my 2 stock HU connect to High level input. Off course not turn on new and old HU same time.Amp is Focal Solid 4. 
I think that is the cheapest way to connect 6 CD changer, Navigation CD receiver, and new HU(maybe Pioneer deh-6350)

Or get a processor!

in more laymen terms:

passive = set/tune 1 time and thats the end of the story, less headaches
active = option to tune it anytime you want, however, headaches as you may most likely be tuning it all day erry day

yo guys.i'm driving old satria 1.3.
no door speaker.now only got dashboard speaker.
the dashboard got wire for dashboard 4 inch speaker.
i'm thinking of diy tarik wire to the door.
so normally if ask accessories shop to do,they make a new wire from the socket or just tap from the dashboard speaker wire?

Technically you should be pulling the wire from your HU / crossover to the door.

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?

Now i know..
Yesterday i cabut the grounding its still running.
Then i cabut the antenna,the player mati.
So,antenna is supplying the ground.
No wonder reception not clear..
How to eliminate this ah?
I want the grounding from player to one point independently..
No other ground point..

my old Alpine is dying
CD still plays fine, but radio often blacks out for no reason. need to off the player for a few mins and on again only it'll restart

anyway what i loved about the alpine is the sound quality, esp when playing cds. now if i need to get a replacement HU, what is the best SQ type HU for a budget of about RM300-500?

or within that budget, all SQ is same, just difference in features?
thanks!

Or my bling bling Panasonic double din!