What is the difference between the ReadyNAS Duo v1 and v2?

Well, I checked the FAQs and that's the wording of the question I need... but unfortuately the answer is blank, so hopefully I'll be forgiven for asking here...

Basically - I'm in the market for a home NAS and am pretty sure I need a ReadyNAS Duo (2x2Tb). However - I see that there are both v1 and v2 versions still available, and I gather they are fundamentally different and that it's not necessarily as simple as just going for the most-up-to-date version? I'm not at all sure which I should go for, and would be really grateful for any advice. From what I've learned so far, I understand that:

v2 allows for larger drives (may be useful for me in the future I suppose)
v2 has a USB 3.0 port, rather than 2.0 with v1 (not sure I'm fussed - certainly I have no USB 3 devices yet)
v2 has faster file transfers than v1 (has to be a good thing?)
v2 doesn't support use as print server via USB, unlike v1 (bit of a shame)
v2 has fewer add-on modules available (dunno whether this is an issue for me?)

My projected use is as follows: Central availability of files (MS-Office etc) for multiple computers; streaming of music/video to a Western Digital media player; streaming of music to a Logitech Squeezebox; storage of iTunes music for multiple family ipods; possible remote access to files.

One thing worrying me is this add-on module thing - I'm not sure what all this means. For example, there appears to be a Squeezebox add-on for SPART, but not ARM (ie v2 but not v1) - see http://www.readynas.com/?p=4248. So do I need this module? Will I be compromised by buying a v2 with no Squeezebox add-on? This is one personal possible issue I've identified, but I'm sure there's more - HELP please?!!