What is involved in putting an 8" driver where a 6.5" driver used to be?

Not to overstate the obvious.... but mostly what is involved is ROOM. If the 8" speaker will physically fit into the space where the 6.5" used to be, you are home free. You will most likely have to use a tool like a Roto-Zip or ?? to enlarge the hole where the smaller speaker was. Don't forget to take into account the fact that the 8" speaker will be deeper than the 6.5" original, as well as larger in diameter.

I am not interested in subs, which is why I am suggesting the 3way set with the 8" midbass.

If I can offer a humble opinion here... you would be well served by installing at the very least a single 10" subwoofer. If you put it in a minimal-size box you can play it right through your rear seatback if it is reasonably acoustically transparent, and not eat up too much of your trunk space. The improvement in your sound quality and enjoyability of the system will be far greater than the inconveniences involved in doing this.

Any comments on the amp?

I don't know a lot about amps in general, nor that one in particular, but if it says Sony on it, with a suggested retail of $599, and is only 200 watts -- that pushes all my hot buttons! You tend to get what you pay for in car stereo, and a $600 amp that isn't promising kilowatts of output power is very likely spending all that money on output quality instead -- definitely the way to go.

tanstaafl.

"There Ain't No Such Thing As A Free Lunch"