Try the following and see if it solves anything for you:
1) complete uninstall & delete all folders and files in reference. Use a program like Revo Uninstaller to assist if neccessary (google for a link)
2) once clean, reinstall BG (sans totsc)
2a) use a custom location rather than the default location. this is especially true on the Windows OS
Example: C:\games\Baldurs-Gate
3) initialize game settings -- do this by:
3a) run config.exe and set any features that you want, else go with the default
3b) start the game, create or import a character, allow the prologue intro to play
3c) once you are at the game screen with your avatar available to use, exit the game (no need to save)
4) install ToTSC
5) repeat step 3 and pay attention to the version # which should be located in the bottom left of the options screen
6) if not version 5512, install the correct patch for version 5512.
6a) there are US English and UK English versions to know which one to use open the readme.txt file that came with the game
(if it is the UK version the readme will say that it is, if it says nothing then you have US English)
7) repeat step 3 again to verify the game works
8) repeat steps 2 thru 7 for BG2 SOA & TOB substituting proper version numbers, directories, etc...
OPTIONAL (but strongly encouraged): backup your game. don't need to really back everything up, but it's real easy to use 7zip, WinRar or similar and compress the whole game into a backup file. Will come in handy if you find major problems with the game later on after having installed multiple mods.
9) after everything is tested and works out of the box, EasyTutu may be applied.
9a) I recommend using the EasyTutu beta installer. It is real simple and easy to use
9a1) go to this thread
http://forums.pocketplane.net/index.php/topic,27712.0.html read at least the first post and the fourth post. links are in the fourth post.
Any issues after doing all that, report back with what happened and at which point in the process.
Also if you still get a request for 'disc 6' after installing the ToTSC patch, put whatever disc has the ToTSC content in the drive, it should accept that.