I have pretty much always used a mixer between the system and the pa.

Small mixers (check out Behringer web site)

have a mid setting at about 2.5 (Mid range knob)

You can roll off some of the highs and lows and boost the mid.

Bit of a challenge for me, I have to have other ears, I hear absolutely zero above 2.7 and up.

But, the xenix series of mixers (and others from say Mackie), all have eq.

If you are talking about only the band in a box output and wanting to boost the mid range your computers should offer you some eq for that signal.

I don't know where you live, but here I could take my laptop into a 'music' store and try some mixers. I strongly feel that usb based mixers are the way to go, but to each his own. I do know that for the eurorack non usb type mixers you can find one for less than $70 and maybe even in the 40 buck range on ebay.

It's worth it to offer a sound guy a few beverages and have him sit in on your gig. The guys here each do 20 or 30 big shows with 48 ch. mixers and mess with eq all the time. You have to be cautious to express your wishes before hand. You probably are not trying to be a heavy metal cover band, and thus want sound levels through the venue that make sense.

The owner/manager has some say in that too.

I'm almost useless that way due to the hearing loss, as nothing can be done, I have not heard someone use the letter s for over a year now. Due to eq and compression I only understand sports on tv, due to the fact only men usually talk. Don't try and explain that to anyone of the female persuasion. Too bad I can't hear the birds either LOL.

Keep plugging, one day the answers become easier.

There is good info in eq'ing on the Musician's Friend website.

John Conley
Musica est vita