I believe a 92 EX cassette deck was capable of controlling a changer... do you have a picture of the stock deck? That way I can tell if it is capable. Your best bet if it is changer capable, is to get an alpine M-Bus changer and an alpine to honda adapter cable... that will just plug into the rear of your honda radio and the changer controls will be operated through the buttons on the stock deck. Does your honda cassette deck say "CD" on it anywhere, like on or above a button? That would indicate it is changer capable.

you will not have to replace your speakers, only if you want better overall sound from all your sources. There will be a noticable difference in sound quality from cassette to CD.

There is also a single CD player that will fit in the lower portion of the dash opening... crutchfield sells them, for around $200... or you can find the Honda OEM units on ebay for a lot cheaper... this is also assuming your cassette deck is changer capable. If it is not, you can upgrade to a 94-97 accord OEM cassette deck, it will mount and fit just like your oem unit, and is changer capable. They can be found for pretty cheap... I'll sell you one for $20, they can also be found on ebay. They will also just plug into your factory wirring harness in the dash... so there is NO compatibility issues.