Just completed my full blown alpine install and the results are dismal..
The system:
IDA-X305S receiver
PDX-5 Amp
Type R 5 1/4 componets in front doors
Type R 6.5 coax in rear doors
JL power-wedge 12"
Monster 6 channel RCA connect
Ran quality 12 gauge speaker wire from amp to all speakers
8 gauge amp wiring kit
Had the gains set by a pro..
Bass,,,, sux
Highs,,,, Piercing
Mids,,, have no ambiance
Seriously, the stock 8 speaker system actually sounded better. Any suggestions? Other than put the stock crap back in!!!
I would say first of all, spend some time with your system, don't give up immediately. Let your ears adjust, etc. Sometimes people think that the new system sound scuks because it sounds 'different' from what was heard before.
A lot has been suggested already, so I may end up repeating things here..
Bass:
First of all realize that you can get only so much bass from a 5-1/4 woofer. What can you do to improve bass? I would say, first sound proof your doors. There are several tutorials out there. I prefer to apply a few tiles of vibration dampener to the outer door skin, and then seal off completely the middle section, with a layer of closed cell foam on top, creating a kind of an infinite baffle for the speaker.
Second, play with speaker phase. Try flipping the phase of the subwoofer. First play a track with good midbass content, flip the phase, play again. Keep the subwoofer wired in the mode that had more impact.
Next, consider getting a better subwoofer. If you intend to keep the 5 inch speaker in front, getting a lot of midbass from them could be challenging. At the same time most car audio subwoofers do not have that great of midbass because of high inductance, etc. Most of them are designed to produce high impact sub bass. What subwoofer could work well? Dayton Reference HO and HF, JBL WGTI, Peerless XXLS and XLS, and a few other subwoofers. Generally, when a subwoofer has inductance close to 1mh or lower, that's a good indicator that the sub will play some nice tight midbass should you consider using a high crossover frequency. Now you won't see this spec provided very often. When its not provided you can assume it's bad..
Music: as others had said, try to play the highest bit rate mp3 files you can get. I personally prefer to rip all of my CDs into flac format, which is lossless, and then export from flac into 320kbit mp3 files for using in car players, etc. Likewise, I hardly ever download anything from the web in mp3 format.
Amplifiers: A lot of 5-channel amplifiers can be a little weak on power on individual speaker channels. Try to do this experiment.. this shouldn't take long. Disconnect the rear speakers. Check the manual to see how the speaker channels are bridged. Bridge the channels and power your front speakers this way. (note that, you probably need to get rid of one set of RCAs, and split the signal of the front RCAs into two... check the Alpine amp manual first) If it sounds better, leave it like that. If you like to have rear speakers, connect them directly to stereo's amplifier.
Highs: Have you played with the tweeter attenuation settings on alpine's tweeter crossovers? They go down to like -6dB or so.
Ambiance: My preference is to make the front speakers play most of music and keep the rear speakers attenuated just to provide some ambiance. This specially works well if your head unit has time alignment. First time align the front speakers with each other, the best you can, so that the human vocals are in the center of the sound stage. Then _delay_ the signal to both of rear speakers by approximately 15-20 ms (as opposed to time aligning them with fronts). This creates a sensation of the sound waves reflecting off the rear wall and coming back at you in a larger room. Next, turn them off completely with fader control. Play some music, start increasing the volume played by the rear speakers until you feel like the sound stage starts floating backwards. Stop and back down a little to eliminate this effect. Now you should have a system with decent imaging, and good ambiance. This is what I used to do. Rear speakers are important for good ambiance. Right now I have switched to running an active front stage. There is no way to run active front AND rear fill with my equipment, so I don't have a rear fill for the moment. While I am enjoying the current setup, I am really missing the ambiance provided by rear speakers. I am currently considering adding a new amp and some kind of DSP (MiniDSP, MS-8, etc) to get my rear fill back.
I have owned the older 6 inch Alpine Type-R speakers, SPR-17S and in my view they had plenty of body. Midbass sensitivity was nice but it wouldn't take a lot of power with low crossover frequency. The midrange was powerful. I could listen to them for a long time with no fatigue. However, the new ones are 100% different, so I can't comment.