The DMF is there to reduce the cars NVH values.
In older cars the flywheel was solid and the clutch itself had springs in it, these helped damp vibration and noise between the engine and transmission. Some twonk decided that if they turned the entire flywheel into a spring mounted plate, then they could reduce that further. Most cars with DMF's subsequently have a solid clutch disk, and the DMF does the damping. Some models however, Like the S4, have both a DMF and a sprung hub clutch, presumably to smooth things out further.
If you convert to SMF, you need to fit a sprung hub disk if your car doesnt already have one, and i suspect this is the issue dmsclark mentions. The 30v 2.8 has a solid clutch, so it couldnt be used with a Single mass flywheel. You'd need to buy an S4 clutch instead (which is lucky, because no such easy option exists for 1.8T owners).
The main reason for conversion is that the DMF's have a tendancy to fail. Instead of it just being a lump of metal on the end of the crank, its now a moving part with springs and gears etc. Seen as you've ripped the whole car apart to get at the clutch, it seems a bit silly to leave the flywheel in there, as even if its fine now, it could easily fail before the new clutch does costing another wodge.
FWIW, the flywheel on our 1.8T finally started showing signs of failure at 190k. It jammed one morning, which made pulling away a horrible juddery affair (no springs in the clutch and no springyness in the flywheel) and stayed like that for a few weeks before unjamming itself. The clutch was original (had nice audi logos all over it) and when i pulled the engine at 193k it was almost down to the rivets.
I replaced it with a TDi flywheel from and Audi 80 and a clutch from an early A4 Tdi so i had the sprung hub, but that doesnt really apply to the V6.
I have to wonder if its a wise decision to spend nearly a grand, fixing something that isnt actaully broken, to cure a problem that you might not even cure. The bite on ours was very high, and did move down with the new clutch, but once the clutch bedded in the pedal has raised up a again. Its not quite as high as it was, and its much more progressive than before, but its still high.
