Cross, U-Mix Control Pro 2 and Master Volume issues

Question 2 of the day.
For some time now I've had this issue and I just can't figure it out. I feel like I must be being a n00b DJ!
Every mix I record is a lot quieter than any other audio track I might listen to.
I've experimented a lot and I can't push the Master Volume in Cross any higher without tripping the volume warning indicator on my U-Mix Control Pro 2 - and of course I can see me hitting the reds in Cross.
It means I'm always having to adjust the Master Volume throughout a mix...now "Gain" I hear you shout. If I have the option ticked, isn't Cross supposed to manage this between tracks? I feel like it really isn't.
I'm willing to be taught a lesson here, whether it's just how to manage this in general or technically with Cross and my controller. But at the moment I'm getting really frustrated about 1) Low overall mix volume and 2) Noticeable differences in volumes between tracks.
PS Nearly all of my tracks are purchased from the iTunes store, or at the very least all good quality so I don't think this is the cause.
For some time now I've had this issue and I just can't figure it out. I feel like I must be being a n00b DJ!

Every mix I record is a lot quieter than any other audio track I might listen to.
I've experimented a lot and I can't push the Master Volume in Cross any higher without tripping the volume warning indicator on my U-Mix Control Pro 2 - and of course I can see me hitting the reds in Cross.
It means I'm always having to adjust the Master Volume throughout a mix...now "Gain" I hear you shout. If I have the option ticked, isn't Cross supposed to manage this between tracks? I feel like it really isn't.
I'm willing to be taught a lesson here, whether it's just how to manage this in general or technically with Cross and my controller. But at the moment I'm getting really frustrated about 1) Low overall mix volume and 2) Noticeable differences in volumes between tracks.
PS Nearly all of my tracks are purchased from the iTunes store, or at the very least all good quality so I don't think this is the cause.