Hi easternnihilismfront,
I also have a Coli 300 with a Sunn 215 cabinet and it is very loud and perfect for gigging.
You might consider using the Coli 300's Bi-Amp option to get more highs if you have another bass amp with some smaller 10" speakers to get the tone you are looking for. That is how I use my stack where the Sunn gives me the nice warm low tone and I use another bass amp with a 410 cabinet on top the 215 for a more crisp and brite tone. In fact, the Coli 300 manual suggests using and experimenting with a guitar amp for Bi-Amp mode to get some bass highs. I have also tried with a Fender guitar amp that has 2 12" speakers and it sounded great.
Good luck!