Depending on the synth/patch, -7.5dB max might be normal/fine, especially if it's a monophonic patch. Even for a polyphonic piano or something like that, -7.5 is plenty of level, and you should probably just turn up your monitoring system.
But if you really need more output from the synth, you can either go into the synth's interface, and drag it's output level fader up, or you can split the Simple Instrument track ( I assume that's what you're using), and drag the MIDI Volume fader up to 127, which will control the output volume of most synths. But some synths are capable of going to +6 or +12dB, whereas MIDI volume 127 will only take them up to 0dB. This is a problem with the synth programming. In that case, you'll need to use the interface control and leave the MIDI volume in the track disabled (value in parens - right click and choose to disable if it's been activated)
If all else fails, you can get more volume by increasing the input Gain and/or output Volume of the audio part of the Simple Instrument track above 0dB. The volume control in a Siomple Instrument track is audio output Volume. The autiod Gain control can only be accessed if you split the track to separate MIDI and audio tracks (or go into the Track Inspector).
Whatever you do, don't mess with MIDI "Gain", which is just a velocity offset, and will only serve to decrease the available dynamic range.
Clear as mud?
