Install a QSC amplifier instead.
Up-market cables and connectors aren't going to make any difference to
the sound quality over standard ones.
I haven't seen a rock-ola digital and don't have knowlege of it
specifically, but as a starting point,
You will have a fault with either computer, amp, crossover or
speakers,
About all I can advise is, if you have a known good juke, swap these
over until it comes good.
failing that, if its in the workshop and you have a known good CD juke
there / good stereo system take the audio leads straight from the
computer to the input of the amp in the other machine and see how it
sounds (disable the mute too so it will play). If its ok, then you can
eliminate the computer as a problem and look into the amp, speakers
etc.
also check the "graphic equaliazer" and "room pre-sets" (ie:
"concert", "auditorium" "theatre" etc) in windows "sound
properties" (if available on this system) and with the amp too.
If you know what you are doing, you could connect the speakers in the
known-good system to the amp in the bad machine and see how it sounds
to eliminate speakers as potential problems.
check to make sure that all speakers are working, loss of connection a
tweeter etc could make it sound awful. Check that there aren't any dry
joints on the connectors (if any) to the crossover, or the amp,
speaker terminals. I have had bad connections and terminals be
vibrated, "open and closed" by bass (woofer) vibrations, and this can
produce some strange sound :)
Finally, (and I hope this isnt the case with yours)
The very few modern (1990's-00) CD Rockolas I have heard didn't sound
as good as AMI CD jukes in my opinion, so this "problem" may possibly
be "normal" ?.