Mike-
I believe all you need to do is buy the Pioneer player and connect the Front L&R output to one of the inputs on your receiver. Go into the menu and turn off the other channels (center and surround) and set SACD playback to read only the 2-channel layer on the SACD disks (I'm assuming they all have 2 channel layers. Not talking bout the hybrids, just a 2 channel mix of the SACD coding? Someone correct me if needed).
DVD-As are not (usually) encoded in stereo so it will be an artificial mix running through your 2 channel receiver.
Speculation: If you use the stereo out on the player to connect to the receiver, you will get an artificial DVD-A mix. If you use the Front L & R outputs on the player to connect to the receiver, you may only hear what was meant to come from the front mains in the DVD-A coding. What is supposed to come from the center and surrounds will be lost. Turning off these channels in the menu may fix this, but I am not certain. (Again, if this is wrong, someone correct me).
A few pieces of advice:
1) If you do buy the player, only buy SACDs with a 2 channel layer until you are ready to upgrade your receiver. The DVD-As will be a waste. If you are serious about getting into these new formats, upgrade to a surround receiver with inputs that support them.
2) Use the Pioneer for all playback, it will probably be the best quality player you own (although I am not familiar with the DVD player, it should easily outperform the CD player).
3) Upgrade your speakers everntually to take full advantage.
Good Luck