I own a vy ss commodore and currently i am running 6.5" jbl gto splits up front and 6.5" fusion 2 ways in the rear running off a 4 channel blaupunkt amp (BLAUPUNKT GTA 475 Car amplifier)
... What setttings should i have on the stock headunit bass trebel ecttt also what about the gains on the amp? at the moment the sound is off the bass out of the speakers doesnt sound to good... This sat im getting 2 8" subs installed so that should help..

Stock HU = limited adjustments

Bass & Treble Setting is totally up 2 u. No one can say how much, its pretty much as per user's preference... as long a the sound doesn't distort.

GAIN setting - take a look at the beginner's guide in the forum and follow instructions... pretty straightforward.

8" Subs - I'll leave this to the others... i suppose its going 2 b installed on the parcel shelf in place of the fusion 2-ways?

My suggestion is to leave the settings in a stock HU, just pure flat 0 for bass and treble etc.

To get a good solid bass out of ur splits, u should deaden ur doors

For the gain on the amp, set the volume level in the HU say like 20, then set the gain from the amp starts going up from 0 till u hear a distortion on ur splits, then thats ur max volume (for example 20 from ur headunit) u should go when u crank up ur system