Yes, I think the upgrade is $500 so used unit upgraded to DSD would be a good route. It costs a bit more if you do not have the Hi-Res option installed. Comparing the two, old and new QB-9 would probably not work since the DAC chip is new??
Here is some info on the QB-9 DSD:
I think the first units will ship next week, and the US retail price is going up $500, from $2750 to $3250. We were going to keep the price down by using less expensive master clock modules (one each for multiples of 44 and 48 kHz), but in the end decided to go for the gusto and just put in all the improvements that we made to the DX-5. The DX-5-DSD will still sound a "bit" better as the analog circuitry and the power supply are more sophisticated. The changes to the QB-9-DSD include: 1) Changing the DAC chip from the Burr-Brown DSD1792A to the ES9016S. 2) Replacing the audio master clocks with low-phase-noise modules running at twice the frequency of the previous ones, which allow the ESS DAC chip to perform at a higher level. 3) Changes to the analog audio circuitry and its power supply that improve the audio performance. 4) Addition of an AC line powered supply for the USB circuitry. This provides for uniformly superior performance, regardless of the quality of the USB Vbus power supplied by the computer. 5) The ability of the USB Audio input to accept and decode native DSD files from computer sources. The updates will take a long time. We can only do five or ten a week and there are thousands of QB-9's out there. You'll just have to be patient... Thanks, Charles Hansen Ayre Acoustics, inc.
The original location of this info is in a thread that is hilarious. Some dipsticks argue with Charles about DSD, happens later in the thread. I can't believe how much Charles responded and the incredible amount of information he provided.