I'm very picky when it comes to the clarity of my sound. I want extremely clean highs and mid-range, and crisp bass (not boomy).... the speakers I always try to fit my car with (if possible) are JL Audio. However, the size and space you have to play with on the front dash speakers are a bit harder.
I read several posts on MB Quartz, and let me tell you, they're pricy, but worth it. I installed the MB Quartz PVI-210 series for my front dash, which include a 4" woofer, and 1.5" tweeter.
For the doors I replaced the woofers with the JL Audio ZR 650CSi's. Although they also come with 1.5" tweeters, I chose not to install them.
I also wanted a completely "factory" looking soundstage, but there's work involved in order to achieve this.
If you plan to upgrade the dash speakers, the first problem you'll come across is that there is a special "basket" fitted to the OEM speakers.... the only way to remove it is to essentially rip it off, saw it off, etc.... I didn't prefer that method. Instead, I unbolted the original woofer and tweeter from the basket and set them aside. Then I took my 4" MB quartz woofer, and surrounded the edges in an industrial strength velcro fitting to temporarily hold it in the position I wanted. Then I sealed it in with clear silicone and let sit and dry for about a day. The Tweeter I did the same thing..... I also chose to use the crossovers that come with the kit to ensure that my highs and mid-range were separated properly.
As for the door speakers... you'll again notice, that the OEM speakers have a "special" encasing, and unless you use the same specification speaker size as the OEM, you're going to have difficulties upgrading them. I made my own custom "speaker encasings" made out of 3/4" Oak Plywood. There are several articles out there on the exact specifications you need to cut and fit these yourself. In addition, I wrapped the entire surround in Dynomat before fitting the new JL ZR 650 woofers. I also used the ZR Crossovers again to ensure these speakers were getting 'just the lows.' After I fit and re-wired the speaker in the baffle, dynomatted the baffle, and screwed it to the door, I then Dynomat'd the rest of the door to ensure there was a good seal, and sound proofing. (I have an article out there on my complete re-work).
For a while I used the standard HAES 6 channel amp that you have, but decided that the way it was setup to handle the rear speakers and door speakers was not properly staged. So I replaced the amp with 2 JL Audio Amps located in the front trunk, and did a complete re-wire. Other than the amps, it has a completely stock look to it. I then later added the Alpine IVA-W505 Head Unit, because I wanted bluetooth, NAV, and XM capabilities. With the available installation kits out there for the AVIC series head units, it allows the new head unit to really blend in to the dash and give it that updated look without looking like it's cheap or "non-factory."
I also upgraded the 4 rear speakers to JL TR 350s but that's neither here nor there since you don't plan to upgrade those.
Driver's Door Complete
Passenger Door Complete
Amps Complete
Head Unit Complete
My 2 cents.