I can't get audio channels to sound dry.

I use MainStage 2.2.2 to play software instruments from a Midi Keyboard and sing using MainStage effects. My problem is that even if I have no effects or sends on the audio channel strip, the sound from the microphone is not clean. It's like whatever comes in to the mic is somehow dubbled, making a chorus-like effect.

It's not the Shure Beta 58A microphone. It sounds perfect connected straight to a mixer. It's not the Apogee One audio interface. I get the same problem connecting the mic via a mixer straight to built in audio plug.

I thought it could be my early 2008 MacBook Pro 15" being to slow. So I tried different buffer settings and it did infact make a difference. It was set to 256 and if I reduced it to 64 or 32 it sounded better but not good. But the the CPU didn't handle it very well so I had to go back to 256 to be able to at least play the software instruments. But it clearly had something to do with latency. And thats a mystery to me since the signal shouldn't be processed at all.

It's exactly the same in Logic 9 and Garageband when used live, but anything recorded sounds just perfectly right.

I've now just bought the new Retina MacBook Pro 15" with 2.6 GHz Quad-Core i7 and 16Gb RAM thinking that it should fix the latency. To my surprice it didn't. I have exactly the same Roundtrip and Output latency as with my old computer(!?) and I still can't get audio to sound dry. I've set buffer size to 32 and the faster CPU seems to handle it but it's still not dry. I'm also very disappointed that some of the effects are still useless with Audio Channel Strip latencies up to 100 Ms, exactly the same as on my old computer.

So my questions are these: Why is the sound affected by MainStage even if I just whant it to go straight through? Is there a way around this? Am I doing something wrong? What kind of super computer is needed to use some of the effects without latency or making a untouched audio channel to sound dry? Why is the latency the same on my new (10 times faster) computer?

Sorry for the long text but it's hard to explain this problem.

I'm very thankful for any help.