You need a high powered head unit to make any aftermarket speakers sound good.
This is so very true. I have three different head units in all three Jeeps. I have moved around the 2 12" memphis subs in all three and they sound the best with the Sony Xplode unit I have. It has good power, plus I'm able to independently control the subwoofer level, not just the 'bass'.
Kenwood head unit.
Sony X-plode tri-mode amp (65w x2, 150 x1) under rear seat.
Infinity (can't recall if Kappa or Reference) 5.25 co-ax in the doors, powered by the head unit.
Blaupunkt 6x9s in wedge boxes, and a 6" Bazooka tube in the back, powered by the Sony amp.
I 'm running a Sony X-plode head unit and X-plode 6.5 inch speakers for the front doors and rear sound bar. They fit right in the sound bar, but for the doors I raised the speaker mounting holes up slightly to center the speaker. No trimming necessary. I also used the harness adapters for the head unit and speakers, so it was plug and play.
'97 XJ Moss Green Metallic. 2DR. 2WD AW4 tow pkg.,3.73 gears. Firestone Destination A/T 225/75x15.
I already have a pretty good head unit. My stock speakers are trashed now so hence the need to upgrade. I noticed the little amount of space for the door speakers. Did any of you run into clearance issues? I'll just be doing the four speakers for now and see how they sound. If I feel like I need it, I'll put in a sub and an amp to run it all. I want it all to sound good, and not just bass blasting my ears.
60% of the time, it works every time.
Choosing speakers is mostly based on quality of materials and how much power they need to be able to handle. There are minor variations in frequencies put out, but especially for someone like you, that's irrelevant stuff. Make friends with Crutchfield.com. They make shopping very easy. If you tell them your vehicle, they'll show you everything that fits and even stuff that will fit with a little modification (they tell you which is which), and if you order with your vehicle info put in, you get an installation sheet tailored specifically to your model and, probably, some installation accessories for free. They also have reference material on their site that explains all that you want to know and more.
Honestly, if your original speakers aren't broken, just replacing them with aftermarket speakers isn't going to make that big a difference all by itself. If you get a higher powered head unit or, even better, an amp to power aftermarket speakers, things will sound better. If you also install crossovers to block the bass that small speakers can handle and to block the treble that subwoofers can't handle, everything will sound way better.
Don't be afraid of subwoofers. For some reason (idiots who install huge subs cranked to max and nothing else) people seem to think that subwoofers are evil, annoying bass machines. If you want to hear the low frequencies at all, you NEED a subwoofer. The little 5.25", 6.5", and even 6x9" speakers in vehicles physically cannot produce sounds below a relatively mid-range frequency. You can force them to try, but your sound quality will suffer greatly for it. A single 8" or 10" subwoofer should be more than enough for yousince you're not a crazy audiophile, and you'll save money and space that way.
What I'd do:
Head unit with all the features I want regardless of power output; it will NOT be powering the speakers.
Some 5.25" speakers or 6.5" speakers/components for the doors. Rated to at least 50 watts RMS.
Put 5.25" or 6.5" (if possible") in the sound bar. Again, at least 50 watts RMS.
A decent 5-channel amp with at least 50 watts RMS to the 4 speakers. It's better to have an amp more too much power for the speakers than to have an underpowered amp; you can always turn the gain down on a more powerful amp.
You really need to be careful when choosing your front door speakers. The stock speaker depth is 2.25 inches and you cannot go more than that without the clearance issues with the window. There isn't much out there for speakers with that shallow of a mounting depth. I installed jl audio c2 525x in the front door, these are 2.5 inches deep and I knew that when I got them, I made a spacer from 1/4 inch MDF to push the speaker out and I have no clearance issues. It is a tight fit when the door panel goes on, but there is no interference at all.
All the XJ's I have seen have 5.25 speakers in the back as well even though online and at car stereo places they will tell you they are 6.5 inches. You have some freedom here because the rear speakers mount into a plastic piece, it is easily cut to make larger speakers fit, which is what I did, I installed jl c2 650x's out back. Honestly you will be glad you went with something bigger than the 5.25's, you need a larger speaker to move all that air back there. Even if you decide to go with a sub, you need good sized speakers to give you the mid bass response a sub cannot provide.
I also installed the alpine amp, http://www.crutchfield.com/p_500KTP4...ower-Pack.html, behind my alpine head unit, and for the and simplicity, it works great and had a noticeable improvement in sound quality. Being a student, money is always tight and this setup is definitely a massive improvement over the stock system without having to invest in a bigger alternator, better wiring, amps, blah blah blah.