The offerings from PGMusic sometimes cause a little confusion.
First of all, the basic BIAB program is exactly the same in every PAK you buy; it's not like some programs where they remove programmatic features based on the level you buy. The difference is in the number of MIDI styles, RealStyle, RealTracks, RealDrums, and SuperMIDI Tracks you get.
The entry level version of BIAB is the ProPAK. A number of folks on the forum have been after PGMusic to rename this, as Pro tends to imply "top of the line". The ProPAK is actually the entry level version of BIAB. It gives you just enough content to create some songs, understand how the program works, and get comfortable with it. For people that like BIAB, most will upgrade it to one of the other PAKs after working with the ProPAK for a short period of time. The ProPAK gives you about 300 RealTracks (grouped as RealStyles, or Bands), a handful of SuperMIDI tracks, and some of the MIDI Styles. This is the lowest cost package.
Next is the MegaPAK. This gives you more content. You get about 500 RealTracks, also grouped as RealStyles (Bands), a few more SuperMIDI Tracks, but you do get ALL the MIDI styles.
The UltraPAK is next. This basically gives you most everything (but not everything). You get all the RealTracks and RealDrums (except a few that are offered with special PAKs), all the SuperMIDI Tracks, and all the MIDI Styles.
The Audiophile edition is basically the same as the UltraPAK, except that the RealTracks are uncompressed WAV files instead of compressed WMA files.
The PlusPAK is a special case. It really only applies when you already have the previous UltraPAK. What it does is takes the previous UltraPAK and gives you everything new to bring you up to date as if you had the new UltraPAK, without buying the UltraPAK upgrade. It assumes you have all the previous content. The web site is pretty clear that the PlusPAK requires the previous installation of the UltraPAK (or previously also the EverythingPAK).
If you currently have only the ProPAK, and you can afford it, I would upgrade to the UltraPAK, and then when the new version comes out, upgrade using the PlusPAK.
However, the downside of doing PlusPAK upgrades over the years is that if you ever have to re-install, you have to first install the first base UltraPAK version you own, and then apply each PlusPAK in turn until you are up-to-date. If you do an UltraPAK to UltraPAK upgrade (which costs more, but is fully self-contained), you pretty much have everything already in that new UltraPAK
Hope this made sense:+++ HERE +++
is the link to the various Windows packages offered.+++ HERE +++
is the link to the various Mac packages offered.