PA Issue @ Practice

[MetallyGuitarded]

Hey guys, I have a PA issue I'm hoping to get some help on. I'm not sure if any of you can help but I figured you'd be as likely to know as anyone...

I can't seem to get the PA loud enough for our one and only vocalist to hear himself over the band at practice. He's the ONLY thing going thru the PA. Here's what I have, in order it's connected.
Mic: SM-58
DSP: TC Voicetone Synth pedal ( before the mixer )
Mixer: Yamaha MD-8 ( Multi-track Mini Disc console, using one channel as a channel strip only )
Amp: Crown XLS 402tx ( 260w @ 8 Ohm, 400w @ 4 Ohm per channel )
Cabs: 2 x Community MVP15 15" 2-way

Possible root cause - The MD-8 has RCA outs only and the amp has XLR ins. We currently have a Hosa RCA to 1/4" patch cable going into non-transformer 1/4" to XLR adaptors.

With all levels dimed it is too quiet and we get occasional clipping which leads me to believe we have adequate signal levels. I'm just curious if the Impedance mis-matches are to blame?

I've tried running the speakers/amp bridged/mono which is over 500watts and it's no better.

 

[arv_foh]

Those cabinets are 500w program at 8 ohms. You need a bigger power amp, it's far better to be overpowered than to be underpowered and clip the shit out of the amp, risking blowing your drivers and such.. You are only feeding those cabinets half of the power they need to reach max SPL

Go buy a Behringer EP2500 (450w per channel at 8 ohms, enough for your situation) or an EP4000 (550w at 8 ohms, ideal for your situation) and thank me later. And before anyone talks shit because it's Behringer, go read all the favorable reviews about these amps on the web. They provide good, clean power. I have 2 of them pushing subs in my FOH system at my venue. The price will not kill your wallet either Nate.