What you need to be careful of here is whether your 673 has adequate bass control for the speakers you're thinking of. If the receiver isn't up to the job, the speakers will lack punch, and bass will be ill defined resulting in a dull sound for both music and movies.
The RX6's aren't short of bass, and this usually requires a fair amount of control by the AV receiver. As good as the 673 is, if you want to be looking at £1,000 floorstanders, I would go for a more capable receiver like the RXA1020 or the outgoing RXA1010 if your budget is tight.
As well as the RX6 and 2050i, you could also look at the Tannoy DC6T (standar and special edition) and the KEF Q700.