Between the E50 ant the D70Pro: there is a difference. I did a test with voicemeeter so I could switch quickly between the two. TheD70Pro sounds a little more airy, and the bass ever so more defined to my ears. I'm certain I would not be able to distinguish between them in a blind setting. Some people might, kudos to them. If you own an E50: no need to upgrade, really. I only did the upgrade because of the looks, and I can afford it. The D70pro has some more connectivity and Bluetooth, which I genuinely appreciate. People don't understand how it is possible your modern, multiple 1000€ system has no bluetooth

As for the Yamaha: since I am solely listening to digital (laptop/CD-transport to DAC to amp) I was using just one input on the integrated Yamaha. I really like the looks, but I had grown disappointed with the sound, especially the bass weight and control, as well as midrange clarity. When watching movies I often had trouble understanding dialogue. Also it was taking a LOT of space, and drawing 75W just idling (they don't mention that in the brochure) The Audiophonics solved all that and more. Effortlessly transparent, weighty and tight bass at any volume, sparkling highs without fatigue (on my Wharfedale Lintons) And: the power! It draws a few watts idling, and by the time it draws 75 Watts, you're no longer listening but seriously angering the neighbourhood.
For me this is as good as it gets. Not harsh at all, I would even go so far as to call it musical. the hype is real. Class D is the future. I have always liked bright sounding systems. I heard Accuphase and Luxman amps do the same, but (no surprise here) at many times the cost. Only downside: it's an on/off machine. Volume control via the source or DAC. The E50 does a good job, but the small silver device on top of my, now black, amp wasn't really doing it for me in the visual department. Plus I like myself a rotary knob. The D70pro is an indulgence for me, but the OLED is so good that VU-meter looks just real, with a nice warm yellow glow. And the knob turns. 12v trigger for one button system on/off. What else is there to want?