Are there any preamps that can work with 2 amps and a sub woofer?

I have a Krell sub woofer and 2 Llano trinity amps powering my speakers.  I'd like to know the best way to have 1 volume control over the whole system.  Currently I have to control the sub separately (manually).
Does any preamp allow 3 outputs?   Is there a better way?  Should a go with a good preamp and just split the output?
Thanks for any ideas.