How can you hear if there's a lot of jitter in a recording ? And what is the top limit of jitter(in %) to make a good recording (where the jitter is very little or not audible at all) ?

And does anyone have a suggestion for a drive/burner to measure C1-C2 and jitter for audio cd's (that are in sale now).

There's only really the BenQ DW1655/DW1650/DW1640/DW1620 which are getting very difficult to find because they are no longer produced.

A Plextor Premium2 CD-RW or Plextor Premium CD-RW drive, or Plextor PX-760/755/716/712 is also a good CD scanner, but jitter scans are much harder to interpret. These drives are also no longer produced.

The third choice would be a LiteOn CD-RW drive, which cannot show jitter and unfortunately tend to almost ignore even deliberate damage to the CD, or a NEC/Optiarc drive which cannot show jitter and can show random C1/C2 spikes at many scanning speeds.

I can't think of really good CD scanning drive that is also easily available.

They sell the Philips DVDR1668K at a store near my place. Couldn't this drive be "converted" to a BenQ 1655 ?

According to this thread, the answer is "yes".