Yes, the Coliseum amps are oddballs. The tone controls are really more like non-graphic equalizers, essentially separate channels for each frequency band. They don't interact the way traditional tone controls do. I remember reading that John Entwistle used Coliseum amps to biamp his rig; he just turned the low tone controls up and the high controls down for feeding the 118 cabinets, and vice versa for the 412s.
Thud, maybe your Coliseum might sound better fed by a Sansamp or similar.