I would be glad to help.
To begin can you tell me the make and model of the bluetooth audio device and the computer that you are having this problem on?
Can you try playing videos on a few different web sites like youtube.com hulu.com vimeo.com and let me know if you experience any problems on those sites?
Have you tried connecting another set of headphones or speakers to your computer to see if they exhibit the same problem with your iTunes files?
I see. Based on those test results I would suspect the issue is with your Bluetooth headphones ability to decode the audio of the DRM-protected content in iTunes. This is why you cannot reproduce the issue from other media sources or other headphones. First I would try reducing the distance between the headphones and the bluetooth receiver. Also, I would remove the Bluetooth pairing entry for your headphones from the Windows Bluetooth settings and try repairing the headphones. If that doesn't work you may need to purchase a higher end bluetooth receiver. Also do you know the manufacturer of the headphones? There are currently two different Bluetooth headphones with that same model name. I'd like to check the manual of the headphones to see if there are settings to change the way DRM content is received.
Great. After rereading my post I realized I might have been unclear what I meant by "repairing the headphones". I meant to reestablish a new pairing with the Blluetooth receiver, not physically repairing the headphones in any way. Sorry if that confused you. Let me know if those suggestions do not resolve the issue.
Did re-pairing or reducing the distance of the headphones help eliminate or reduce the audio delay? If not, what is the make and model of the headphones? There may be a way to change how DRM audio is decoded using buttons on the headphones.