Installing an aftermarket radio on an I30

[A33 Cefiro]

All right, so after 100 AUX tapes, I am fed up with the stock bose system. I don't care how good it looks to keep it stock, I need an AUX input. With that being said, I have finally decided to install a head unit I've had laying around for a couple months now. I've done aftermarket radio installs before, but never had I dealt with ground issues as complicated as this one. I will be buying the Metra kit. The trim with the radio clips and the converter that will allow my speakers to go through RCA. My question is though, where do I ground the whole system? I already know where I'm grounding the HU but I've been reading on various forums that the wire kit will have 2 wires that I need to ground somewhere. Where should I do that? Also, is it true that placing the speakers on RCA cables lowers the volume to the point that it's noticeable?

Some advice would be appreciated. Thanks.

[AppleBonker]

Do you have a link to the metra kit you will be using? I am a bit confused as to where the RCA cables are going from/to.

As far as grounding goes, you should be able to ground everything to the same spot behind the unit. That is what I've done before. I doubt there will be a whole lot of current, so it shouldn't create any issues.