[Biturbos4] 0-280-142-116 (and turbo loss)

[Grant]

Hi all,

I recently lost boost in my 2000 S4.  Stock, mostly.  I remain 
optimistic that my turbos are healthy since I don't beat on it, use 
Mobil1, and cool it down religiously.  Also heard no singing, and the 
car ran almost OK even without boost.  Just lethargic.

I began investigating, suspicious of the TBB, when I found (wish I 
could post a pic, but I cant - if you want to see, I can send them 
direct) that the 1/4 vacuum hose between a mysterious black cylinder 
and another was frayed and torn.  A bit more digging revealed that it 
has also pulled out of its hose (loose clamp I guess?) which connects, 
with ~1" hoses, from just pre the TB to the intake to the turbos (the 
pipes leading down from the air intake).  Each is marked BOSCH 
0-280-142-116.  Topologically, they could be bypass valves.  Are they?

Now, this could just be a loose clamp and if I put it all back together 
with new hoses, all might be well.  But while its apart, what's the 
advice on testing or replacing these devils?

Any and all educated advice welcome!

Thanks much in advance,

Grant