I listened monitor audio Rx6 + NAD C355 combo for over 2 hours. I went for the audition with lot of expectations. but believe be, not good musical experience. new RX series is not good. i found bookself RX2 better than Rx6. But still not upto the mark..
The bad experience you had was the result of wrongly partnered equipment with the RX6. Y'see the new RX6 is a step-up from the RS6 in the treble department where the former has a rolled-off trouble, meaning, they'll never sound bright, kind of laid back sound, which in itself is unique for MA speakers, but that's the new RX6.
So, now, the NAD across their range is known for their warm and never-bright sounding signature. And, if you're gonna pit a NAD to the RX6, I don't know where the excitment is going to come from - pretty much bland music is the result.
Let's bring in the old RS6 to gel with a NAD amp, then we're talking about excitment and musicality, hope you can my drift ?
Some amplifiers than can bring life to RX6 would be Naim, Cyrus, Marantz, CA (740 and 840).