Get some test pipes and a nice axleback. That will give you power (TPs) and a better sound. I am running the Fabspeed x-pipe with HFC and resonators with a Dinan rear section. It is only slightly louder than stock, better tone, and no drone (I'm not bullshitting here either like most people do, I've had 10 exhaust setups in 14 months).
If you did TPs and the Dinan rear section, you'd have basically the same set up as me for ~$2K (if you can find a used Dinan) and you'd be very happy.
2008 IB E92 M3| BBS | KW | Arkym | Platte Forme A.G. | Active Autowerke | K&N | Fabspeed | Dinan | Evolve-R