Wow. Now I kind of regret bringing it up. I thought I was cutting edge, but I am actually obsolete.
The market segment isn’t obsolete and I think perhaps Drobo might have been early (or at least it’s the first brand of its type I heard anyone talking about) but now there are several companies in the business.
If Dropbox works for you, that’s great. I was going to recommend you check out Backblaze.
Given your setup, you probably can’t use the $7/month unlimited data, since you’re dealing with network drives. But I do believe they are competitive in the professional space, too. And there are some nice perks, like the ability to get a 20 TB mailed do you, which you can get your money back after you return it.
For personal backup, I recommend Backblaze, period. For your case, I just think it’s a company worth looking into.