Probably the best archive for old analog is digital, but then you'd want to keep it in a couple if not a few different places and ensure backward compatibility and store as higher rez consolidated files to be safe-r.
Right now I work a lot for the departmental conservation, I transfer all of their archives (1/4 inch tape, cassette, mini-cassette, DAT, Minidisc ...).
In addition to create numbers of inventories, we use this method :
- 1 HD file
- 1 MP3 file (to listen everywhere and sharing online)
- 2 referenced audio CD (each stored in different locations)
The whole is transferred to two hard drives (also stored in different locations)