"HDMI switching only" means that it cannot process HDMI signals for BOTH Video & Audio. It can only carry the Video signal. You need to hook up the audio signal separately--Optical, Coaxial, Analog 5.1 inputs, etc.
If all you want is DD or DTS, then Optical or Coaxial digital audio is great.
If you want Dolby TrueHD or DTS-HD, you need to get a blu-ray or HD DVD player with internal TrueHD & DTS-HD decoders and send that PCM analog signal to the 5.1 analog input of the Harman Kardon AVR-147.