Wish,
Here's an alternative that might be worth thinking about....
As you will have discovered, the best sounds for BIAB backings come from using Realtracks. This is because they are audio recordings of the actual instruments. Moreover, the audio is played by world-class musicians. MIDI, on the other hand, is digital data that instructs synthesisers (software or hardware) to play a particular sound. Some of those sounds (like piano, organ, strings) can sound incredibly realistic with a good synthesiser. Many other sounds, however, do not have the same level of realism. For example: In my opinion, guitar sounds are generally ok but have not yet reached the same realism that is found with (say) piano.
With the above in mind...
Historically, PG Music release a new version of their Windows software in December. This has always been accompanied by great deals. Change-over prices from earlier versions of the software at this time usually offer great savings.
If you want to get the best sounding backing tracks, you'd be better off to invest your dollars in upgrading from the ProPak to the UltraPlusPak; the UltraPlusPak is the first package that contains everything. That way you will get every Realtrack (over 2,000 of them) and every possible style.
Below are links to the specifications of the two packages for comparison purposes.
ProPak information...
http://www.pgmusic.com/bbwin.packages.pro.htmUltraPlusPak information...
http://www.pgmusic.com/bbwin.packages.ultra.htmIn short, what I'm saying is that in about one month's time, it's highly likely that PG Music will release a new version of BIAB (we never know in advance but it's been happening every year that I've been on the forum, since 2008). When this happens, great deals will be available and you'll be able to get a package that contains everything at a good price. Maybe that's a better option for money investment since then you will not need to by any add-ons.
Just another thought.
Regards,
Noel