I'm not entirely sure why anyone would use
Reason 5 or below as a master tool or in judgement for a final mix. Reason just wasn't for that, hence not introducing Mastering Suite/Combinators till
Reason 3. Cubase, Pro Tools & Logic Pro are far more advanced and adapted to mastering songs a lot more intrinsically then a midi based program and that's the fundamental difference between all DAWs and sound quality.
The method I use; I write midi and audio using Reason, then mixdown and personally master stems on Cubase (for DJ purposes) then get the track mastered professionally for labels, internet, TV, etc. Tracks can be mastered for as little as £10 and most EDM labels expect you to get your tracks mastered before being signed.