The Flat-Cap2 provides 24 volts (from both its supplies, even though one is "secondary"). In contrast, the NAPSC is 18 volts (or somewhere around there). Unless the stageline and/or prefix have an internal regulator dropping their voltage needs below the 18 volts, then it's highly unlikely that you could use the NAPSC to power either one. Additionally, the NAPSC is not a very "quiet" supply, so it would probably sound bad regardless.
If you're looking for a cheap supply, get yourself a used SNAPS. I'm not sure if the Stageline or Prefix use both rails from a *-cap. If they do, then you'll actually need a SNAPS2 that's been converted to dual rail. Unfortunately, the only sure way to know if a SNAPS is really a SNAPS2 is to look inside the case to see if there are two regulators. If the conversion has already been done, then the pre-amp supply supply will be 5-pin. (A regular SNAPS has only 4-pin sockets.) Catch you later!
-=> Mike Hanson <=-
