I think it is intended that you cannot keep sound turned up while using a metro app in the background (iheartradio is what I'm specifically using). Is this something that I can get around or is it just annoying everyone and we all have to wait for an update?
This is how I understand the technical side: Metro is originally designed to "disconnect" apps from continuing audio/video when switched to the background; there's a Technet (?) paper around that describes this default behavior as a user-friendly decision to prevent people from getting confused if something starts playing in the background and they have a bunch of apps running. However, it is possible for app developers to program their apps to continue playing audio (described here, though a bit out of date for 8.1).
Under normal circumstances, if an app isn't programmed to actually do this, the default behavior naturally has precedence. The only way around it is to snap the app.
But in this case, D1vad says it continues to play for him, so... Check for app updates?
Yep just installed iHeart radio in the last hour. Audio is working on the Metro iHart app, while reading in the Metro Kindle app, Or in Metro, weather or metro IE. It also keeps playing while dropping to the Desktop and launching IE from there. Hasn't stopped playing at all in the last hour. No matter what I've done.