Everything is possible, but real cost might be surprising for that kind of project.The C300 I think have decent drivers, good crossover and absolutely superb cabinets and stands.
I wonder actually whether there would be a way to keep the cabinets and stands and go for a big upgrade with some really high end drivers and upgraded crossover - possibly even make them active - I do have a spare DDRC24?
Would that work? I can't particularly see why not.
In fact, what you are looking for is to re-develop new speaker based on the drivers and cabinets you have. It is exactly same job what will be done with new speaker development.
Here are 2 way you have:
- study and jump in deep DIY speaker building yourself , it will be just your time to spend on your hobby, result is unpredictive as in time too in final sound
- send speakers to someone engineer, who can do this job paid. Quite expensive job, which consists of the following tasks:
0.0 completely disassemble speakers
0.1 measure TS parameters of drivers
0.2 check right port alignment and cabinet volume for woofer
0.3 mount drivers back to cabinet with "wires out"
0.4 measure electrical and acoustical parameters - impedance and speaker response
1.0 prepare files for crossover simulation software
1.1 create some crossover model
1.2 solder crossover prototype
1.3 measure impedance and acoustical response
1.4 if response within desired curves, go to listening tests, else to 1.1
1.5 listening with various music, amplifiers in a properly treated room
1.6 try different components (different type of capacitors, resistors, coils, wiring, terminals) to find best matching combo to desired sound + budget
1.7 If satisfied, go to 2, in not to 1.1
2.0 solder final crossover board
2.1 assemble speakers
There is a loop of iterations between 1.1 and 1.7 - this process is science and art,
it included very technical and scientific tasks and listening tests what is more related to how we listen and enjoy the music, not the highs, tweeters and woofers, but how musician want to show his work of art.
There are may speakers what looks technically superb but sound boring or irritating and much less speakers in the world which gives us a joy when we listen to the music music. Both might be very good technically and the difference in frequency response might be just fractions of dB, but how this difference distributed in whole spectrum matters a lot.
Assume, that whole process may take from 2 weeks to 6 month to get speakers sound right, and just multiply amount of hours spent to engineer's salary+taxes, you'll see that costs might be quite restrictive for such upgrades, and parts costs (original cabinets + drivers for Q - good, but not that good as high-end drivers from SB Acoustics, Scan-Speak and Seas), might be just a fraction of total costs and it target is to get state of the art project, would be better to go to better drivers and new design and get even better speakers then upgraded Q.