Good news and bad news, everyone!
The good news is: You know that Rockman X Anniversary Collection soundtrack we've been hearing about the last little while? Apparently it's now available to purchase on Steam! Here's a video Capcom posted with a sampling of the tracks:
What's more, soundtracks for all eight individual games are available as well!
Now, the bad news: It's apparently considered downloadable content for Mega Man X Legacy Collection 1 + 2 on Steam, meaning that you have to buy the collections in order to buy the soundtracks, which are available there in AAC, FLAC, and MP3 formats.
There is an iTunes option here, but it's just for the Mega Man X Legacy Collection soundtrack (though it appears the others are available from prior listings -- check the thumbnails at the bottom). What's more, Capcom Unity's Patrick believes that this only gets you the AAC format.
In addition to the cost of entry with the purchase of the games on Steam, the Mega Man X Legacy Collection soundtrack runs $17.99 USD, while each individual soundtrack (which requires the corresponding half of the two-collection series to purchase, i.e. you need Mega Man X Legacy Collection 2 in order to purchase Mega Man X8's soundtrack, for example) runs $9.99 USD.
For track listings, more details, and the favorite songs of several members of the Capcom staff, check out the full post on Capcom Unity.