Well... confirmation number one, Pioneer (VSX53) was the worst of them, stereo speaking. I've tried it (and some others) on plenty of occasions, always that same harsh sound... It's always "surprising" in a way, as the same receivers do so good with HT... you'd just expect to get about the same with music... still wouldn't be THAT good, for in my experience stereo soundstage is always quite narrow when using A/V amps... But the truth is Pioneer they always sound worse.
Yamaha RXA1010 is better. Of course it is a great HT amp just like Pioneer, but even more, Pure Direct mode will give you a clear upscale in sound when in stereo, and offer some smoothness (compared to Pioneer's similar function at least). Still, you can easily notice that the amp put some strain on analogue sound. Mind you, I was playing CD's in a Blu Ray player (Panasonic BDT310) for both Pioneer and Yamaha, and if I'd never consider upgrading for a decent CD player with Pioneer, I certainly would with Yamaha. It might REALLY help!
Arcam AVR400... it comes as no surprise that Arcam might give you the best musical presentation of all three brands, still with the same blu ray player... but a very shifty quality with HT at that price. And the Amp functions and display just look cheap in a way : no volume knob, but two simple +/- buttons... not responsive. It takes hours to turn it up or down by hand... Takes hours to change source, and don't think about pressing the buttons quickly, you HAVE to wait three seconds each time you press it. Yamaha RXA knob is like steering a great car while in a drift, it just wheels around smoothly and responsively, and sticks to your finger without you even thinking about gripping it. I wouldn't care about the buttons if I was only using Arcam for movies, as I would always use the remote... But when beginning to play music, I like to stick around the amp for a while, just play with the volume and feel the amp response closely. It's just a habit, I'm sure I'm not the only one... and Arcam AVR won't let you have that pleasure. In fact it is better to stay in the clear, and use the remote, because the more you look at that cheap row of buttons closely, the more you hate it.
So, RXA-1010 or AS-500... well, it just depends on your most fundamental needs : HT or music?