The Duo is also Sparc based like the NV+ (basically the two systems are the same, just one has 4 drive bays instead of two).

If you want something more powerful for home, you could look into the ReadyNAS Ultra lineup. They have 2, 4 and 6 drive variants, and then the Duo could go to Andy's house for the remote backups.

If you want to run encryption, it looks like it's possible to use Duplicity on the ReadyNAS. This works like rsync where it only sends over the differences and can mirror, with the added benefit the remote copy is encrypted. The Ultra CPU should have more then enough power to handle this decently.

If you do go the ReadyNAS route, let me know. I have both an NV+ and an Ultra 4 at home, and can do some experiments to help find the ideal setup. Assuming Andy can take care of the networking part on your side, this should be pretty workable. A bit of setup effort, and the process should run smoothly for as long as you need it. All you need to decide is if you want a large up front cost (new NAS and drives) and no monthly fees, or if you want to go a service route with no up front cost but monthly fees.

One other possibility to toss into the mix for monthly service is the ReadyNAS Vault.

*edit* Seems Andy and I are thinking alike, both posted the Duplicity solution at the same time