upsampling HDCD?

I would say no..
http://web.archive.org/web/20030625224915/www.musicalfidelity.com/a324upsample.html#frameint

As I recall HDCD conversion was licensed by Pacific Microsonics without whose chipset HDCD decoding is impossible. Part of the contract specified that redbook CD's play back at a lower level than HDCD's or something like that. As an offshoot, HDCD's played back over non-HDCD equipped players sound louder which, in addition to their inherent quality, make them sound more impressive. Sorry that's not much help. I suppose the question is: does Pacific Microsonics do upsampling?

The upsampler treats the HDCD as just another CD and doesn't do HDCD decoding.

The HDCD process starts with 88.2 khz sampling of the original signal at 20 bits (if I remember correctly...) followed by a kind of "perceptual encoding" process that decimates the original bit stream to 44.1 khz, applies mathematical processes to encode wider dynamic range in the 16 bit data stream, and encodes the least significant bit in each sample to tell the playback system which inverse process to apply to restore the original 20 bit wordlength.

The playback system uses a perfect conjugate filter to the original lowpass filter used upon sampling, decodes the the low order bit pattern, and applies the appropriate mathematical process to restore the 20 bit data stream (or some reasonable facsimile).

The upsampler ignores all this.

THere are no licensing issues when playing an HDCD disc on non HDCD equipment.