OK I borrowed a better meter... testing the ground between the two main speakers, with the dial set at 200 the reading was .8 set at 2K it read .001
am I reading it correctly? so it is a common?
Use the meter to test the resistance at the two negative outputs on the amp. if your reading around 1 ohm, you have a common ground amp. Most receivers are common ground.
A word of advice from a long time SDA owner, that receiver won't do those speakers justice. I would use a separate preamp/amp combo. You'll need more than 100 wpc to make them sound their best. Those speakers are around 5 to 6 ohms, most receivers don't do well with a speaker less than 8 ohms. If you have a set of preouts on your receiver, run those into a separate amp. Those Polks will sound much better.
Placement is also very important. They should be set up in an equilateral triangle, no toe in. Each speaker should be two or more feet from the side wall to sound best. The speakers should be around 6 - 10" from the wall directly behind them.
Set them up right and give them some good clean power and they will amaze you!
Good luck!