Thank you to "LikWidChz" for submitting his tutorial on receiving and decoding multiple NRSC5 (HD Radio) channels with the help of GNU Radio, a HackRF and the NRSC5 decoder. He writes:

I wanted a way to utilize GnuRadio for working with HD radio. There are no decoder blocks from within GnuRadio to perform this decoding without an external application. This write up is how I was able to split up some signal and supply NRSC5 what it requires to perform the decode.

My goal was to capture some slice of spectrum and "channelize it" so I can perform multiple HD radio decodes at once.

In this linked zip file we have uploaded his GRC file, and his tutorial PDF, which fully explains each GNU Radio block used, and how to use the NRCS5 decoder along with the flowgraph. He also notes that if anyone wants to get in touch with him he is idling on IRC in #gnuradio and ##rtlsdr on freenode under the nickname "LikWidChz".