Is this Crown XLS 402 blown, or impedance mismatch?

[RedfoxRambler]

I recently bought a Crown XLS 402 on ebay for an odd rig: I'm running an Ampeg PF-20t all tube 20w bass head through an Ampeg PF-115HE 1x15 450w 8ohm cab with tweeter, for vocals (dynamic mic to mic preamp) and acoustic guitar with K&K pickup (hooked up to preamp), both combined with a Morley ABY Mix pedal then into the Ampeg. It sounds really good but of course the 20w tube amp only goes so loud and sometimes I need to supply sound for gigs at bigger places, plus I'd like to be able to use the Ampeg rig for loud rock bass at some point and 20w won't be nearly enough. The Crown XLS 402 seemed like a good budget way to make my existing rig much louder.

 

When I got the Crown from ebay and hooked everything up (using line level XLR out from Ampeg head), the only sound I could get when testing with a mic was an extremely muffled, fuzzy/distorted sound when I really yelled into the mic and cranked the preamp or Ampeg volume. I'm using a Speakon to 1/4" adapter, and a quality 1/4" speaker cable to the cab. I can't find a manual online for this exact version of the Crown, I can only find this version which is apparently before they added the Speakon output so I have no idea what ohms that output is at (doesn't say on the chassis either).

 

Does this sound like an impedance mismatch, and if so how would I correct it? Or does it sound like a blown amp and I need to get my money back? Thanks!