I think floresjc summed it up pretty well. I have been using a squeezebox for many years now, and it has a pretty capable little DAC. It took a while to persuade me to get an external DAC, started with one of those little Cambridge jobs that had nice specs and that was OK but the upgrade was subtle at best.
Meanwhile the rest of the chain got upgrades--speakers, amp, preamp. When I got one of Frank's amps, I saw the light.

(Now I have to put on shades)
I thought about ordering a DAC from Frank but the funds were just not there. Then I got lucky and scored a used ultradac a few months ago (funds were probably not there either!). Funny thing happened there--the instant a/b test (using the preamp switch) against the cambridge dac did not seem to make much of a difference. But listening to a song from beginning to end, ah, yes, there is a difference, and it's not really subtle if you pay attention.
Bottom line? I think you can start on Frank's path down at the amp (most people would probably do that) or at the DAC, or at the preamp. In any case, every time you put another AVA piece in the chain, you should definitely hear the "Frank Effect".
If you can afford it, I think it's an easy decision. And if you can't, look at the used stuff! Don't worry, Frank will still talk to ya.

But at this particular moment in AVA history, the combination of lower prices and recent upgrades makes getting a new DAC straight from Frank a very good deal even compared to getting an older model.
So what happens if you call Frank and get the DAC and you don't like it? You can send it back for a full refund, or if you take too long to make up your mind, you can sell it and you won't lose very much money. Just as a for instance, there was an ultravalve that went up on censorshipagon a couple of months ago for about 25% less than a new one, and it went so fast that by the time I saw the ad it was already sold (same-day turnaround). A DAC is less sexy than an amp (though which is more important will be debated!), but I cannot imagine that a similar ad for a Vision DAC would last more than a weekend.