Hi Martin;
MR> So I'm seriously thinking of using it for my electric guitar and just
  > buying a head.  I haven't actually tried this out yet, but is there any
  > reason you can think of why this would be an undesirable combination?
  > I was hoping that it might help give my guitar a warmer, more mid-range
  > oriented tone, which is what I prefer.
I also used a similar setup as you, JBL K145's on the bottom and JBL 
K120's on the top.  The K120's are mounted in TL style cabinets.  They 
sound awesome when used for guitar.  Whether you like the sound depends 
on personal choice of course, so try it and see.
     Take care ...
            Paul
 * 1st 2.00 #1346s * Bass Players are people with lots of depth!
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