OK, I did some more investigating, using your supplied info.
Here's what I get:

- I opened BIAB 2016 (432) with a new, blank song
- Clicked the Jukebox button and set "Generate Solos" to ON
- Set the Preview to be 8 bars
- Navigated to the RealTracks19Demos folder and clicked Play Jukebox
- The "Select Soloist" window opens and a MIDI Soloist is selected (I suppose it's a "random" default as I tried it several times and they were always different). In this case, it selected 56 JPass Guitar.
- Clicked OK to start the Jukebox
- It generated the RealTracks and set the Soloist to be "Guitar_2" (shown in yellow) and then played 8 bars of the first song
- When it advanced to the subsequent songs, AS YOU FOUND OUT, it plays ONLY the soloist, and no other instruments

- I tried the same process, all other settings being the same, only this time in the "Select Soloist" window, I ignored the "default" selection, and instead, scrolled down and selected a RealTrack, 361 Sax Tenor (at least I assume it's a RT as it has a brown background).
- Clicked OK to start the Jukebox
- It again generated the RealTracks for all the instruments EXCEPT the Soloist, which it set to "Trumpet" shown in yellow.
- HOWEVER, when the generation was complete, the Soloist button changed to "Guitar_2" shown in green, and the Mixer window showed (for the Soloist), "Guitar_2" in yellow with the description "361:Sax, Tenor, Jazz Sw 140 (Soloist)"
- It actually played a Sax solo, and not a Guitar
- I tried this a number of times with similar results, sometimes the Jukebox wouldn't "advance" after 8 bars, despite being set to do that
- Sometimes the songs wouldn't Juke at all, it would just stop after the first song

All in all, I can confirm that the Jukebox DOES NOT work well when trying to use a RealTracks Soloist.

Good luck!
LLOYD S