I have a Yamaha RXV750 I was thinking of mating to a 7125 or 7075. How would this sound vs a 1070 receiver? Speakers are Tannoy Saturns which are rated at 6 ohms.

Not having compared the two directly, it's always hard to say, but there's always room for a bit of speculation...

Is it safe to assume that the 1070 be operating alone rather than with one of those amps? If it would be alone, I think it would be a tight race, with the edge likely going to the 1070 unless the Tannoy's are very inefficient and therefore needing the extra power of an amplike the 7125. The 1070's processor sibling (the Model 970) edged out the Yamaha RX-V2500 (operating as a pre/pro) in Doug917's comparison test , but any receiver with the "heavy lifting" off-loaded to a good amp should sound better than the receiver by itself. Based on that, the 1070's pre section should be a nice upgrade from the Yamaha, which could be enough to offset the benefit of an outboard amp on the Yamaha.