Replacing drivers in studio monitors?

A friend of mine, who has a home recording studio, blew the drivers in both of his Alesis M1 Mk2 audio monitors. He was in the middle of a project and bought some upgrades right away. Long story short, he gave me his old "blown" M1s for free. These things are/were nice as hell! They MSRP at $600 and go for $400 in stores.

Each is self-amplified, so I'm thinking of hooking up my empeg dock to them. I am going to contact Alesis on Monday to see how much replacement drivers are, but I'm not going to be using these things in a recording studio, so I am entertaining the idea of just getting some 6.5" drivers to pop in there to save some money.

Does anyone have any experience in this? Is using off-the-shelf drivers a bad idea?

Specs:
Low Frequency Driver: 6.5" non-woven carbon fiber with Santoprene surround and dual magnet shielded configuration.

I think you would need to find out more of the specs of the original drivers (like frequency response) so you can find some that are similar.