This Project began to explore the use of the DVSI AMBE 2020 voice compression chip and also the ADF7021 single chip VHF RF Transceiver from Analog Devices.
http://www.moetronix.com/dstar/
Speakers Simulator is a freeware Winamp plugin to simulate a loudspeaker-like soundfield in your headphones. I think you have already noticed the difference between speakers and headphones.
http://headwize.com/projects/showfile.php?file=kopjov_prj.htm
You can also use the cheaper TOTX178 (left pictures), but the optic wire should not exceed 5m - the both other ones (173 and 176) can drive up to 10 meters.
http://www.boehmel.de/dbox2.htm