How to Convert Stereo to Mono without losing Music volume

Achieving good mono compatibility whilst mixing in stero is a bit of a black art... what exactly is it that you want to mix? Typically, anything like speech, which is generally panned to the centre will come out fine, but anything where the difference signals are significant (like stereo music where most instruments are panned away from the centre) will inevitably come out quieter, as the centre channel sum signal will not be as great. It's not unusual, when it's a real issue, to do a separate mono mixdown with the levels adjusted. This is fairly straightforward to set up - all you need to do is depress the 'sum to mono' button on the master channel, and temporarily adjust the individual track levels, where needed, to achieve a better-balanced result. Then just mix that down, and save it to a new file. Yes you'll have two tracks (it is a stereo session) but they will be identical, and will sound just as you remixed them.