The NAS will only appear in the Finder if it resolves the machine name. It's probably still there. Imagine a heavy bird fell on my head. Dazed, I would quickly realise I had amnesia. I couldn't even remember my name. I'm still there though, look it's me in the mirror. Think of it like a heavy bird has fallen on your NAS. It's there, but like some bizarro version of Cheers, no one knows its name.
That said, I'm a bit puzzled why iTunes still doesn't recognise. It should still be mounted in /Volumes. I think. But if not, then there's your problem, iTunes is shouting out a name, but bird-thunked NAS doesn't know that's its name. "You mean me?" it ought to ask. But computers are dumb, and that's not just because heavy birds fall on them with what appears to be troubling regularity.
So, I figure two options.
1. Remove the name issue – if you NAS seems to like being 192.168.0.70, you can simply mount the drive by cmd-K and smb://192.168.0.70 (long term though, if you rely on IP, then you ought to set a static IP or reserve the address at your router, there's nothing otherwise to stop another device claiming that address). If you've multiple shares, they'll list in the following dialogue. Click the one you want. Don't mount anything from the Finder, you'll confuse things. Anyway, fire up iTunes with option key held down and find your library on the drive you just mounted. See if everything works as it is supposed to.
2. Don't use SMB (on the Mac). Instead connect via AFP, which is a Apple-specific file sharing protocol. Most NAS (and a far as I can tell, iOmega) support this though you may need to enable it. This should place the NAS back in the Finder (as it'll be using Bonjour for name resolution). You may get two entries (one for SMB and one for AFP) – click the AFP version (if in doubt, right click and get info, the location should "afp://" rather than "smb://"). Set up iTunes as above, with the library on the AFP mounted drive. Your NAS should happily share files with Sonos via SMB and your Mac via AFP.