In the thread I cited, Albert mentioned Michael Percy at www.percyaudio.com, who could put together the resistors you need.
He also mentions something simple: the Channel Islands Audio vpc-3 Passive Controller. It essentially functions as a volume knob for your Celeste HT3. Once you hook it up (with interconnects--nothing technical), you can lower the output of your bass amp to match the output of your mid/tweet amp, whatever that may be. Once the vpc is set, you can then simply use the volume knob on your pre to raise or lower the volume on the whole thing. You can probably get some good advice from the folks at Channel Islands in any case. BTW, what amp are you looking at for the mids/tweets?
He also mentions something simple: the Channel Islands Audio vpc-3 Passive Controller. It essentially functions as a volume knob for your Celeste HT3. Once you hook it up (with interconnects--nothing technical), you can lower the output of your bass amp to match the output of your mid/tweet amp, whatever that may be. Once the vpc is set, you can then simply use the volume knob on your pre to raise or lower the volume on the whole thing. You can probably get some good advice from the folks at Channel Islands in any case. BTW, what amp are you looking at for the mids/tweets?