Re,
upgrading the entire IDB from 5.5 to 8.1 will be an extremely involved and painful process. If you can avoid that, all the better. AFAIK you should be able to import DP foreign media into a new installation and get the sessions and objects into the new IDB this way. Provided the new installation has the relevant clients configured, you should be able to restore to them. I admit I've not tested this yet. What I did lately was killing a 6.20 installation on one server, installing 8.11 on another one, reestablish the same clients and specs as existed before (you could count them on one hand, so this was easier and ultimately cleaner than upgrading). With that setup, I was able to import the old tapes from the 6.20 installation and I see all the sessions and objects they contain. What I haven't tested yet is the actual ability to successfully restore, though. So if you are going to 100% rely on it, better test it with a subset of the media first. Also plan for importing tape being a very slow process. Dunno if that also hits virtual tape as it shoud be able to position in virtually no time, but importing eg a physical LTO4 medium takes considerable longer (approx 5h) than just reading it entirely (approx. 2h), I assume through it doing more positioning than actual reading (it's trying to just read catalog blocks and skip over actual content, but doing that apparently takes more time than just reading all the blocks would).
HTH,
Andre.