If you really want more volume, you could also get a pre-amplifer to increase overall volume levels into the existing amps. Likely, your Sony just had more output oomph than the Empeg (which seems surprising actually unless your amp uses speaker-level inputs).

Look at the Overdrive preamp at Audiocontrol for an example..(around $100).

No, I don't work for Audiocontrol. Just a happy customer.