itunes won't play through bose soundlink, but it did before my update today

Make sure you have the latest version of QuickTime (7.6.6) installed - if this is missing or out of date there may be no audio output from iTunes (including, but not limited to, playback through Bluetooth devices) or playback may be of poor quality.

Also check iTunes' Play Audio Using setting in Edit > Preferences > Playback (you will have to restart iTunes for any changes to take effect). In most cases selecting Direct Sound addresses playback issues when Windows Audio Session is active (though some users have reported the reverse),

If neither of these solves your problem try installing this alternate version: iTunes 12.1.1 for Windows (64-bit — for older video cards). The "for older video cards" label is a little misleading, as this also fixes some playback issues, QuickTime and Outlook interoperability errors, and problems with other third-party applications.

I started having an issue when I installed itunes 12.6.1. The Bose Soundlink will not consistently connect using airplay. If the connection is not used for a while (you pause playback for a few minutes, itunes loses the connection and will no longer connect. The only way to reconnect is to turn the Bose on and off. With mine Bose, the easiest way is to remove the battery. When the Bose restarts it will connect with itunes using airplay. Something changed in this version of itunes that is impacting airplay and the Bose. My AppleTV is not having the problem using airplay.

7.7.6 is correct ... typo on my part 😊

Have you tried the other suggestions? The "for older video cards" version of 12.1.1.4 has been reported as fixing playback issues w/ external speaker/devices..

You're welcome 🙂

Did upgrading to 12.6.2 fix this issue? I'm experiencing the same issue with 12.6.1.