Problem with the CDA-9831

A few weeks back, one of my friends tweeked the custom user eq's so I could make the highs higher and the vocals louder via turning the volume up without distorting after volume 23 or so. A day or so after that, the radio vocals went out and just bass tones could be heard. All the wires were checked and appeared to be fine, so we hit the reset button on the headunit and the vocals came back. So then we customized the eq's again, the vocals went out again. This happened about 4 times. Is the problem the way the custom eq's are being set(Not sure how they're set because I didn't do it)? Or is there a different reason why the music goes out? It seems to work fine after I reset it and keep it on one of the presets like flat, or rap, etc. Can anyone help me out setting the eq so the vocals won't go out??

are the highs on an external amp?

if not, and by "just bass tones" you mean just the sub, it sounds like you're overheating the headunit's internal amp and forcing it to shut off, but the preouts are still working which is why the sub is still going. The only way to effectively overheat the internal amp is to clip the hell out of the signal, which is easily possible depending on how high you're turning it and how high you're boosting those frequencies.

Yes I forgot to mention that the interior components(aftermarkets) are on a small 300watt Pioneer amp.

And yes by bass tones I mean just the sub, you can play a song with bass and it will hit every bass tone in the song but no musics or vocals.

when the highs shut off, is the pioneer in protection?

I don't believe so, it's so hard to tell though because that amp is behind the box way in the back of the trunk. There's a blue light that's on but I think it's the power not protection mode, but I'm not 100% sure.