It's a big market and so potential buyers have a wide variety of needs. You might only need a couple of HDMI inputs and some way of connecting the PC, but that might not be the case for many other purchasers. Manufacturers have to try to cover as many bases as possible. That's only reasonable. What you'll also find is that these features come as standard with the sort of AV receivers that can make a decent fist of music.
As for 4K/8K, if and when the dust finally settles and there's a firm final standard for each then we might all face the prospect of having to change our gear to be properly compatible.
You still haven't said anything specific about what "good sound quality" means to you. What have you heard so far that you thought was good? What's your frame of reference, and what specifically are you going to be using as audio sources? For example, are you talking about being able to hear the difference between the sound quality of DVD (DD/DTS) and Blu-ray (Dolby TrueHD/DTS-MA), or are you looking for a surround system that can do music; and if so are you planning on using the Blu-ray player as a music source or the PC. If it is the PC then are these ripped files from your own CD library (and in what file format and quality) or are you streaming from online music libraries, or have you just audio converted a load of YouTube music? As you can see, there's lots of information missing from your queries which makes it difficult to almost impossible to give you any kind of constructive help other than a few random shots in the dark.
Finally, what's a realistic budget for you? I ask that because it's easy to say you want something good enough to blow away the local cinema's £20K rig for detail but if you're expecting that for £200-£300 tops then that would be an unrealistic goal.
Over to you.
