Master Lin says you should practice only one system at a time.
Continued regular practice will put your mind in the correct state. Changing the practice may change where you end up.
It's nice to think you can accelerate your progress, and maybe you can. However, unless you've been there before, how do you know if you've gotten there faster. Then with mental practice once you've learn how to get there consistently, it takes you much less time to get there once you decide to get there.
It's a tough thing to figure out. How do you tell if two people are at the same place mentally? You need to measure, or trust in validity of different people describing something. Which is really hard if you want to know which experience is better.
Using my favourite analogy base Star Wars. Let's take episode I where Count Dooku (sp?) and Yoda are dueling it out. Both seem to be able to control the force equally well, but are they both at the same place mentally. Which experience is better than the other.
I'm not trying to suggest that audio inducers are the dark-side. I'm just trying to point out what I see as a very difficult question to answer. So you may not get a very satisfying answer.
You'll probably get the view point that some prefer to access their states totally within themselves. That their is a potential problem of developing a dependency on external aids to achieve your goals.
Personally, I've chosen to follow Master Lin's teachings. I am concerned about what constitutes studying more than one system at a time. I know that practicing more than one system at a time is against what he says.
You are perfection.
Iam2 
