I took mine to a local electronics store to get the digi-mod. The board was a little too small for my liking.
It's probably easier to just send it to busman to get the whole upgrade at once, if you're planning on going that route. I did mine in two steps, but his mod wasn't available when I got the UA-5.
Eventually, I'd like to send my R-4 to him. He does excellent work.