I'm currently using a TX-SR702 to replace a problem I had w/a Denon AVR-886/2106, which is the next model up from the 190x. I haven't noticed any difference in sound quality, however I didn't necessarily expect to, either. They're similar receivers with similar capabilities, much along the lines of the 703, so I can't see how that would be worth the additional cost unless there's features it has that the others don't.
For speakers that dip down to 4 Ohms, I wouldn't necessarily trust any receivers other than flagship models (or one step down from the flagship receivers) to drive them at high levels. If you've got the room to accommodate for a receiver and the A500, go w/the combo... -TD