This is just my perspective as a customer of JRiver, who does NOT use MC on an HTPC:
* MC is not a set top box, nor is it really designed as one.
* Streaming video services aren't really supported. They can be hacked in here and there, but they aren't part of the core functionality of MC.
* MC has a 10 foot interface like other popular HTPC products, but it's not as customizable and skinable as the others.
* Sonos support in MC has been reported to be a little unusual, as Sonos apparently does not implement the DNLA standard very well. Generally speaking, MC can see Sonos renderers and can be directed to send music to a Sonos renderer. I have not followed any discussions about having Sonos use MC as a DLNA media source.
* MC has incredible media management customization. If that appeals to you, I know of nothing better.
* MC has best in class video quality on the Windows platform. I'm told you can tweak the hell out of it for advanced features like 10 bit video and various upscaling modes. I have no personal experience with this, but the Windows video guys seem to think that MC's video quality is near the top of the top.
Generally speaking, MC is designed for the collector. Someone who has a media collection. Files on local disks that they organize, browse, and play. This includes audio and video files and even images.
* MC's audio support is quite advanced and considered to be one of the audiophile standards.
So that's what your investment buys you, from my limited perspective. MC does a ton of things well. But it doesn't do everything. You might want a set top box for streaming and MC for super high quality video of your local collection. But, if what you said is true, and you have no collection, or a very limited one, MC might not be the proper video product for you.
Still, MC is amazing for audio and might appeal to you on that front.
Good luck with your shopping and decision.
Brian.