1) A receiver is just an amp with a tuner built into it, and 5.1 outputs for home theater etc. You can use it as just an amp if you want to. I'm using a pioneer receiver for my setup just fine.
2) A DJ mixer's output is LINE LEVEL
not phono level. Your DJ mixer has phono preamps in it. So you don't want to be plugging it into the receiver's phono input, because then it will be going through 2 phono preamps. Thats why its too loud and sound like crap.
I'll repeat:
do not plug your mixer's main output into a phono input on your receiver, EVER
Plug it into a line in. On receivers these are usually called "DVD" or "TV/Sat" or "CD" etc (because its for a home theater system). I have my mixer plugged into "TV/SAT".
It doesn't matter. Just don't plug it into a phono input.
Have fun mixing