Trouble with subs and amps not hitting.?

Hi all I have two Kicker Comps 300w 4ohm subs running off a Sony Xplode 600w 4 channel amp bridged all coming off a stock Chevy S10 head unit with the sliced in loc80 rca converter. My subs aren't hitting the way they should what could cause this. I know stock hu's turn the b down to keep the stock speakers from blowing but is there anyway I can get around this without buying a JL Audio clean sweep or something like that I'll be buyin a new hu soon I just want a temporary fix