2007 Chevy Avalanche Ultimate LX stereo?

[Finwick37]

I have a 2007 Chevy Avalanche Ultimate LX with a bose system in it, i wanted to add some subs but wanted to keep the factory radio, so i took it to a stereo shop thay charge me 118 to run the wires and for the part so i could connect my amp and subs yet when i got it home and connect it thay would push i tryed connect a 1500 watt kove amp and one PBX 15, wouldn't push at all so i tryed a a 1200w Hifonics brutus on just a little JL audio 10 still very very little sound or movement from the sub i have had a hook up like this before in one of my older trucks worked just fine tell i was ready to put a new radio in, can anyone tell me what maybe wrong or if thay could have hook its up wrong where it plays but so little that you can't hear the subs at all, i took the truck back to there shop but thay wanted to charge me again when it never worked the first time