Re: Adding 730N and speakers HELP!
There's a lot of variables there. You may just be better off buying an aftermarket Head Unit with Satnav, Sirius and all that stuff than trying to shoehorn the 730N in there.
As far as audio goes, look up PAC audio (pac-audio.com) for steering wheel controls and other goodies. Whether the new speakers are worth keeping is up to you and your taste. Try them out first and go from there but first you have to find out what your existing system has and doesn't have.
If you have an amp you can take the outputs and go to the speakers. If you don't have an amp you'll need a Line Out Converter (LOC) or Processor to convert the signal from the Head Unit to go into an amp then to the speakers. (HU>LOC>amp>speakers)
Usually the only inputs you'll need into an LOC are from the fronts and the sub. If you don't have a sub, the fronts should do as they usually have full range going to them. There are other types of LOCs such as those from AudioControl (audiocontrol.com) which do more and a bit pricier. Depends on what you want and how much you want to spend.
Alternatively you can go with a processor like the JBL MS-8 that is a processor AND amp in one. Albeit a weak amp. So you can go straight out the MS-8 to your speakers (HU>MS8>Speakers). It's tunes your system automatically with a tiny bit of your help.
Of course, there are others out there like the Audison Bit 10 and Rockford Fosgate 3Sixty.3 however these don't have built in Amps and require fine tuning and isn't for the faint hearted. I have a bit of experience in car audio and wasn't prepared to spend the time to do this so after months of research I went with the MS-8. Although I ended up getting an SRT with the HK system so I sold the MS-8.
Depends on how far you want to take it.
2014 SRT - Bright White/Sepia/Pano/HK/Spidermonkeys/Tow/Tint/Injen CAI