Good evening,
I also was waiting for the Marantz with Spotify, but the only competive product on the market - as far as I know - is the Onkyo 9 series (609 / 709 / 809). After reading several reviews about these products, and also comparisons between the new Marantz series and this Onkyo series I didn't find any complain about poorer audio quality of Onkyo compared to Marantz. As both brands are using Class-D amplifiers nowadays, I think the audio quality difference between these 2 brands - if you still can measure this, mainly is *between the ears*.
So I decided to buy the Onkyo TX-NR709. With Spotify and with search function in Spotify! And yes, it really is a GREAT product. Such a fantastic user interface!
I agree with Marantz that searching is a major issue, but as I don't want to use my smartphone or tablet for this function the way forward definitely is integrating these complicated features in the receiver. And how to control these functions? Onkyo already has understood this: they have developed a smartphone app. Not only for the Apple platform, but as well for Android. It is a pity this app still doesn't support Spotify. I guess this will take some time, but I already have tested the first app with Spotify support. Still not working great, but the way I use it today is doing the search & create the playlists on my smartphone using Spotify itself. After I have done this, I start Spotify on my Onkyo using the remote control. And after some time some great app will appear on the market which supports Spotify as you would like to see it, and after some more time you are able to control all your AV devices with an app on your smartphone or tablet.