As I understand it, it's possible to recode the RCD-510 to give line level outputs and cancel it's inbuilt equalising, simply by using Vagcom? Can anyone confirm this method is possible, will work and give me the same quality as the processor route (or near enough)?
You can do this yes. IIRC its listed in the maintenance section in the RNS510 upgrade/setup thread.
NOTHING will give you the 'quality' of a properly setup processor (depending what you class as a processor and quality). But getting someone skilled enough to set it up properly, has the man hours to do it, is another matter but ive been in the ICE game for over 20 years so have different views to some. IMO the JBL MS8 is a great fix and gets the tunning and setup there 90% of the way which is more than 99.9% of the dealers out there are capable of.
EDIT: I missed the audison bitone part as my post was typed as the last two were posted. The audison bit one is a good bit of kit (I have one) but it takes alot of man hours im talking days, of tunning and skilled ears to setup to get the 'best' results.
I find the JBL MS8 solution in 5 mins of auto tune, It got me to 90% of were i wanted to be and saved me weeks of tunning time.
I would say if your into serious world champion EMMA/IASCA soundoff competition then the Bitone has the edge and will get you that extra maybe 10% or less after months of tunning and tweeking you need to go from 2nd to a winner in sound quality but the MS8 i found to get your to 90% or more in less than 5mins of auto tune and make a huge difference to any system even just fitting it inline between the headunit and the oem speakers as it sorts out the frequency responce.