I maintain a user defined library field that can have values CD, Vinyl, mp3, High Rez, Internet Radio, DVD-A. Then I use that in defining the views. You can set the value of the field on import using conditionals, for example set it to Vinyl if the folder contains Vinyl, CD if the folder contains CD, mp3 if file type is mp3 and so on. I also have a Smart List that searches for any track with that field blank. I check that periodically to be sure all are filed. For existing tracks, you can do a search on a given characteristic, like bitdepth =16 and sample rate = 44100 , and fill in the tag tag for those existing tracks. I use a filed name of Media Sub Type Audio, but you can use any field name that is not already used. You could also just re-purpose an existing tag if there is one that makes sense to you and that you are not going to use.
Creating your own library field is pretty straightforward - Tools - Options - Library and Folders - Manage Library Fields - Add New Field.
Once you can your own custom field you treat it like any other tag.
I also use the field name in Thumbnail Text to specify non-CD albums, like for Vinyl rips or Hi- Rez. That makes it easy to identify the source when doing views with mixed source types. I have an All Vinyl view and then, for example for Jazz, I list everything but have a line of Thumbnail Text specifically for Vinyl to differentiate that in the general list.