Holy crap, that JBL set up is a no joke sound system!! It's like, friggin', Back to the Future when he plays guitar, LOL.
Thanks for all you guys' suggestions... I'm really honing in on the Altec Lansing ones, especially with this more 'boxy' design then I can route into a box easier. I've read a ton of reviews on those and they've all been great. Plus, I dig the volume knobs. My 4121's are the next bump up and the sound is unreal but the design just won't work, they're not boxy enough to fit into a speaker hole.
Massive88, so the bass is solid? I really want a lotta punch in mine, especially for that Donkey Kong intro, where it always rattled everything, ya know what I mean? Or, Contra, where you'd hear that intro all the way across the arcade as a kid. The bass, to me, is key. My 4121's would be a pain but they rock... worse comes to work, I could put my current set in and keep the 2421's for my every day use... but they seem like they're gonna be great.
Also, how've you guys been holding yours in? I'm thinking route out the holes on the front, like 1/2" (into 3/4"), then on the back, have 1/4" boxes the size of the speaker, where they sit in, then maybe take some kind of strap and drill it around the speaker box to hold it firm in there, like, going across the speaker's back. I'm curious what you guys have done though.