Just curious, which Teensyduino version are you using? In Arduino, click Help > About to see.
I updated to the latest IRremote for the 1.56 release. As part of that update, I updated the timer defs to use a higher interrupt priority for the way IRremote samples incoming pulses, for (hopefully) better compatibility when using libraries with other interrupts.
I'm pretty sure transmitting with IRremote doesn't work together with audio. Whether that matters, I'm not sure, but it's on a long list of low priority issues. My main concern is whether receiving works well.