Features aside, the 1070 and 970 are in many respects descendents of the Model 950 - which would suggest to me (as a former 950 owner) that the sound quality would be very respectable. It would be an improvement over your old Sony, although having not ever heard your Sony I can't say how significant it would be. My suspicion is that it would be a notable improvement. I made my previous comments about the amp section in the 1070 not so much to point out the extra power as to point out the more robust design - it's likely to yield a nice improvement over the amps in your Sony STR even before you factor in the digital processing section, DAC's, and analog section design.

If you do decide to go separates, there are several good amp offerings available from Outlaw - both the 7075 and 7125 would be great upgrades from your current receiver's amp section. And I can vouch for the 990 from personal experience - it and either of those amps would be a remarkable sonic upgrade from the Sony.