Reading the spec sheet on your DAC/Amp quickly, I see it supports 16 and 24 bit signals at 32kHz to 192kHz. This is almost every format you might want to play and it plays all of them. What this means is, for any file that fits the above rates and depths, JRiver doesn't need to do any conversions. Luckily, by default, JRiver is set up to do NO CONVERSIONS. So for all of those types of files, it's set up correctly by default.
You might want to have a look through the audio setup guide for some basic stuff and for specifics on setting up output conversion.
http://wiki.jriver.com/index.php/Audio_SetupYou probably only really need to do two things:
1. Select the correct output device in JRiver. This is as simple as pulling down the selection box and clicking on the device for the MHA100 in JRiver's audio setup. Tools > Options > Audio > Audio Device
2. Configure the output for extremely high sample rate audio to convert down to 192kHz. The only reason to do this is if you will be playing native DSD content, or if you somehow have PCM files at 352.8 kHz or higher. To configure these outputs:
Player > DSP Studio > Output Format
Look at the box in the lower middle with all of the sample rates. Go to the three rates starting at 352,800 Hz. Click the box next to them and change them to a lower rate that your MHA100 can handle. 192,000 Hz is a safe bet for all three of these rates.
Now test to make sure you can play all of the different sample rate files you have in your library. Include some DSD files if you have any. There's more detail on the audio setup page I linked you to above. But you probably don't need to change anything else unless you experience a playback problem.
Good luck!
Brian.