I'll try to write up a impossibly complicated simple explanation, though the web site itself to grab the files from has clarified the process slightly. However, their steps are still a bit out of order.
1) Download the FIRMWARE_DOC2008.zip file from http://yadi.sk/d/UbPDGP_IKvVCA . Inside you will find a number of zip files, and an update.img file. Ignore the zips for now, and copy the update.img to your DX50s internal memory and install it as you would any other official firmware update. Go to settings -> advanced -> system update. The dx50 will automatically reboot into ibasso's recovery and install the modified update.img. Essentially, this update.img is exactly the same as the stock firmware, except ibasso's recovery is replaced by CWM (both of which are booted into by holding power + volume on startup). Note: Since the firmware file is about 10mb bigger than stock and contains a custom recovery, it will take a minute or so longer to finish the install. If you haven't already copied the cwm_rockbox_2013-03-25.zip to the internal memory, reboot back into the main software and do so now.
2) Boot into recovery again after the update is completed (holding down power + volume up on boot). You should see a new recovery menu with an orange eye and a top hat in the center. The bottom should read CWM-Based recovery modified by androtab.info v188.8.131.52. Now you select Install zip from sdcard, select choose zip from sd card, and select the cwm_rockbox_2013-03-25.zip (mirror at mega.nz) file. It will then ask to confirm the install. Scroll down and select yes, and CWM will install the zip. When finished, return and select reboot the system.
3) Next time you start the dx50, you will get a touchscreen with a choice of whether to launch into mango (the stock player) or rockbox. At the moment, you must launch into the stock player if you want to transfer files over usb.
4) If you want to uninstall CWM and go back to the stock recovery, simply flash the stock_recovery.zip file in CWM and the original ibasso recovery will be restored. I'm not quite sure what the other files are, but they seem to be sound tweaks which are also flashable in CWM, and one of the file contains font tweaks, possibly for rockbox.
Hope this helps, and theres a lot in here to experiment with. Its pretty standard for installing custom recoveries and what not on android, and thankfully isn't the most painful of installs. It is, however, still a bit confusing, so let me know if there are any other parts you get stuck on.
Edited by evilhippie - 3/25/14 at 9:13pm