well....interesting. I do not 'seem' to have either of the files mentioned, though playback works fine.(perhaps those were names in 3.0? and version 5 is different?)
I do have a file called 'quicktime.dll'...but it is in a plugin directory under my graphics viewer "Irfanview" (which will play midi files)
there are files in "C\Windows\system" that seem relevant...especially one named "QuickTimeMusicalInstruments.qtx"
(I use a very good search utility in a File Manager called "PowerDesk"...I will keep looking..)