There are both software plugins (but not sure JRiver supports them) and hardware effects boxes for "tube simulation", but I think you are better off using sound processing software such as audacity to make pre-distorted copies of those specific albums, so you don't need to worry about it at playback time.
Interesting. The only issue with that is that it will take a lot of trial and error work and I would probably end up finding a single setting that seemed to work and just apply it to my short list of tracks.
I currently have Vegas Pro for video editing, but haven't gotten the Sound Forge or Audacity software.
I do see that even my copy of Vegas Pro has a distortion special effect. However I doubt it will provide the control I would like.