I had the standard suspension without ADS (wish I ticked that option now) and although it is comfortable it does toss around a bit. So I am now looking at changing the suspension (shock + spring). However, when talking to some, they recommended that I can change the spring only to Abt spring, which gives a drop of 30-40mm but will not destroy the ride too much, which is what I want. Then some other people that I talked to strongly suggested that I should do the shock and spring together as they claimed that the standard shock is not a good match for aftermarket spring and the shock will go bad after a very short time. Does anyone have any experience that they can share? Thx in advance.

They'll give you adjustment(s) over a standard shock/spring combo. However, I would wait, and let others go first and test the waters of what springs/shocks and coilovers are good,great, bad and ugly!! or at least let the tuners chime in first.

As far as I know, here are your only options for lowering at this point...

KW has coilovers available for FWD only.

KW and H&R have springs available for Quattro.