Why is the volume low while streaming?
You can increase the volume by using the volume keys on your keyboard.
Porthole works with all AirPlay compatible devices, like Apple’s AirPort Express and the Apple TV 1, 2 & 3 (for Apple TVs running software v6.0, update to at least Porthole v1.4.4). But also third party AirPlay speakers, such as the B&W Zeppelin and Denon AirPlay receivers. It even works with most open-source apps like XBMC.
If you want to know for sure, just download the trial first and test your setup.