
How DirectSong works currently.
Gw launch, looks for registry key if DirectSong in installed, if it see's it, then when certain "triggers" it play the higher quality wma file based on the guildwars.ds file (the que sheet).
You can hand edit this BTW

See attached (it's the Guildwars.DS que renamed to txt file so I could attach it). It lists all the music paks but not any of the new factions. I do have the new OST installed.
One of the problems, is the GuildWars.ds (Que sheet) is NEVER updated unless you re-download an existing or add a new music pak. And they have updated several times.
So if you buy OST now, get faction's at launch, it may not use the new sound pack in game unless you redownload the music pak/ost or is Anet changing how it pulls / tracks the file with Factions launch.
Would I would do is make sure you run the GW:F OST downloader after factions launch.