Hi macd
Nice one
as the DSP-Z11 is an excellent amplifier. Out of interest what colour is your DSP-Z11 please?
If you can add a power amplifier later on (such as a Plinius Odean, Bryston 9BSST, etc.) then still look at the 800 Series. If so, then in the meantime try and crossover the sub to the main speakers as high as you can get away with. This is will help minimise the workload on the amp.
What is the size of your room?
Anyway, I've had superb results using the DSP-Z11 with ATC monitors. Curved SCM19's, C3C and curved SCM7's or curved SCM40's, C3C and curved SCM7 are also worth bearing in mind. Alternatively Focal JM Lab Aria 926, CC900 and 906's are also worth a look as they work well with Yamaha AV amplification.
All the best
Rick @ Musicraft