Here are some ideas for a 6-channel amp that can be used in / tailored to a number of applications. The overview block diagram:
The input gain trim can be one of the following. The one on the left gives about +/- 12 dB of gain. I found it in a schematic for a “Sub-bass processor kit” and someone has posted a scan of it here. It’s a variant (much simplified) of the circuit used in parametric and graphic equalizers, where a bandpass filter is insert in the feedback loop. If only attenuation is needed, and a relatively small amount at that, then a pot can be used. Or, for a specific installation, a resistor can be used – or just nothing if no gain trim is needed.
The 6-channel attenuator is a 6-gang 10k pot.
The Buffer/EQ can be what you want. However a BSC (baffle step compensation) network makes sense. This can also be used for a dipole rolloff EQ (withint limits).
The phase/driver block is used on channels 5 and 6 only. It servers to provide balanced outs to drive a more powerful amp. In addition, if amps 5 and 6 can be bridged, a switch is used to select this mode.