Do I use coax, sub or optical with laptop? Audible difference between usb and optical at higher bit rate?
My desktop computer has an S/PDIF coaxial output but I've never seen a laptop with one.
You could get a USB to S/PDIF coax converter and feed 24/192 to your DAC's coax input. Optical is iffy at higher than 24/96 and possibly may not work or have dropouts.
I assume it's a Windows machine, so to avoid downsampling from the Windows internal K-mixer, you need to use a WASAPI or ASIO driver. iTunes doesn't support either of those, so I would also recommend JRiver Media Center as well. Then all formats will be sent to the DAC bit perfect.
What is DSd ?
DSD is Direct Stream Digital as found on SACDs and some hi-res download sites, and you need a DSD capable DAC for those anyway.
I use both iTunes and JRiver. Files are imported into iTunes, then JRiver just monitors the iTunes library folder location. I use iTunes to transmit to casual listening areas over Airport Express and to sync to an iPod, and I use JRiver for critical listening and to sync to an Android phone.
Steve