infrared - IR Audio Receiver and Transmitter

Let me start by saying that I am a newbie on this, trying to do some hobby stuff. I am a software professional trying to interface with hardware (maybe getting into Arduino).

Using this information I was able to build an IR transmitter for an audio device (like my Samsung Galaxy Ace).

Using this information I built a receiver for the computer, captured some input from my TV's remote and built the .wav file to play it in my phone with my transmitter.

It works. Kinda. The range is very short (maybe 3 feet).

Also, I have read somewhere of people adding a resistance because there is a risk of burning the sound card.

I have an old set of computer speakers that have their own amplifier. I am considering connecting them to the output of my phone, and connecting my transmitter to the output of the amplifier. I wouldn't mind if the amplifier died in the experiments, but I am trying to prevent my cell from getting killed in the process.

So the question is, how do I protect my laptop (when recording with the IR receiver) and my cell phone (when playing back with the IR transmitter) from getting burnt?

Thanks.

Note: I know I can just buy the transmitter for the cell phone, but there is no fun on that. This is a hobby project.