I have the 2023 Band-in-a-Box UltraPAK and Xtra Upgrade for Windows
My suggestion is to get the 2024 PlusPAK upgrade. For starters, while there ARE some of the Chinese instruments in the 49PAK, most of them are part of RT set 436 (see image) which you wouldn't get if you upgrade to the Pro. To clarify, you can also add the 49PAK to the PlusPAK. The 49PAK includes a couple of additional Chinese instruments (Dizi Flute, Background GentleSwingReedy sw 110 and Guzheng, Background GentleSwing sw 110 )
The PlusPAK will "only" add somewhere around 12 GB in total to your installation, so you are okay for disk space.
True, it is a lot more than you want but doing it this way will give you everything new and is an easy upgrade, keeping you up-to-date with all available RealTracks etc. so there is nothing missing - just install it into your existing Band-in-a-Box folder.