Youve got the right idea going for those three basic mods at first, but while dinan is a very reputable company, there are some other, MUCH less expensive, options out there.
Since the 6 cyl e39 doesnt have to much of a performance following, your going to have to peice together a muffler and resonantor and essentially create your own catback to save some money. TMS (
turnermotorsport.com) sells reputable mufflers and catback resonators, but they too are pretty over priced. If you can source some parts at wholesale, or possibly get in on a group buy somewhere, you could end up saving a bunch of money over the dinan exhaust.
-You could also go with a reputable muffler and have a tuning shop build you a custom cat back exhaust system, which would probably still save money over the dinan option.
As for the chip, your m52 cannot be chipped because it is OBDII, so a shark injector is in order. The TMS shark injector for the m52 2.8L will be your best bet. You would want to call TMS and talk to them before buying a SI, as i dont own an OBDII car, and im not completely farmiliar with exactly what you will need.
Intake, again a CAI could very easily be made yourself, the dinan carbon fiber one is redicuously over priced.. You could go with the conforti one TMS has, but even that is seriously a waste of money imo.
All these mods will give you some extra ponies, and help with throttle response, but they will not yeild HUGE gaines. Fuel delivery upgrades and cams would be the finishing touch for your motor if your serious about NA mods.. while running your motor on stock internals, besides the cams of course.
If youve got any questions.. fire away.