As the matter of fact, I have both HD-DVD A3 and Pio 400v at home right now and what I can say is they are both displaying great PQ. Out of the box, the Pio settings were a little off but after adjusting it with side-by-side comparison in PQ from HD-DVD A3, I was able to adjust the settings on the Pio to match almost 100% with the PQ on the A3 (IMHO this A3 upconvert is the best before). Of course, I'm talking only with the upconvert functionality of the A3. So now I honestly can't tell the diffence if one of them is playing (standard def DVD wise).
Bottom line is, Pio 400v is a very good player and it can do the upconverting job extremely good and as good as the upconvert from the A3. Now, however, if you don't care about the region free player nor the DivX capability of the Pio 400v, then I would say having the HD-DVD player is more than enough. Why would you want to have another standard def player if you already have the HD-DVD player which does a very good job on upconvert for standard def DVD? In my case I bought the Pio a few months before the A3 so I'm kinda stuck with it :-)
Just my 2 cents,