I run a Sony Headunit in the dash with a CD player with a CB mounted in the pocket below running to a 10 disc MP3 CD changer mounted in the center console. Swapped the door speakers to some Infinities and I am happy.
I don't believe there was a factory changer option in 94, I could be wrong though. And really I can't see putting in a factory changer if it was available as you could probably do all of what I did for just the price of the changer.
I used Infinity Reference 6.5" No spacers. They are inexpensive speaker ($60-80) but sound decent. Butyl Surround with a poly woofer and a good tweeter. I can see spending a lot of money on speakers for how I use my Land Cruiser. The tires howl, the speakers get full of mud and snow, with all of the accessories I get some wind noise. Probably anything is better than the factory speakers.
I actually bought them at Circuit City. I think I paid 69.95 for the ones I put in the 80, I know I paid 79.99 for the ones I put in the 60. The ones for the 80 were on sale. Ultimate Electronics sells them, Crutchfield.com sells them, and I think Best Buy might have them. Also, they seem to go on sale quite frequently (once a month or so). Even at $99.95 they are a decent value in my opinion. Other options that would probably work are the Polks (lower line) and the Boston (Ralleye Series ?), they are all in that general price range.
I went with the pioneer deck that plays MP3 cd's. 1 CD = 180+ songs...so w/random on i only have to change 1 cd every month or so. I also went with 4 INFINITY REFERENCE 625i 6 1/2 inch speakers needed a spacer to make fit..they are snug but sound awesome. Got everything through Crutchfield. It was little more expensive..but, they included wiring harness/mounting bracket for free. I did months of reasearch to find the setup that is right for me. I suggest visit many stereo forums and READ all the comments on the different products out there.
Speaker w/the 1/2 in spacer
Snug fit..but it fits!
They stick out..but you really dont notice them when the doors are shut.
IMHO no one thing makes as big an improvement as a quality subwoofer. I put an Infinity Basslink (powered) in my 80. It has a remote control (wired) and I turn it up just enough to add what 6.5" speakers just can't produce.