I just installed the downconverter board for the netSDR the other day. Works great. Two notes:
1. You need to update to the latest firmware (1.13) for it to be recognized. Once you do this. it "just works" in any SDR app. As soon as you tune above 40 MHz or so, it switches to the downconverter.
2. Update the FPGAs to the latest version as well. Until I did this, I was getting odd behavior from the radio, it would internally reset to 10 MHz each time I left run mode. Once I did that, all was well.
I am still using the HF antenna with this, a 670 ft sky loop is not really ideal for VFH/UHF. There is an option to use another antenna with the downconverter, eventually I will order the a piece of coax with the IPX U.fl connector.