Illustrator :: No Printer Resolution Options For HP LaserJet Enterprise 600 M601

Running under Mac OS 10.6.8, we've run into a problem printing separations to our new hp LaserJet Enterprise 600 m601 printer from Illustrator CS4, CS5 and CS6.
 
In the printer dialog box, once under the "Output" section, with the mode set to either "Separations" or "In-RIP Separations", there are no options listed in the "Printer Resolution" drop-down.
 
I've tried re-installing the driver, changing the resolution settings in the printer itself, using a generic PS driver, and contacting hp directly (their solution was to contact Adobe). I have yet to contact Adobe itself, but none of my other attempts netted a different result.
 
In the document ink listing, the Frequency and Angle listings are still editable, but needs to be done manually for every colour, and the dot shape options are non-existant.
 
We had previously been using a hp LaserJet 2300n, but we were running into insufficient memory issues on an increasingly frequently basis. The driver for the 2300n had several different sets of Printer Resolution settings, so once the new printer was set up, I *assumed* that it would have the same kind of options.
 
I have discovered that if I change my PPD from the proper driver (HP LaserJet 600 M601 M602 M603) to the old one (Hp LaserJet 2300) I am then able to select the resolution I want from the drop-down list, switch the PPD back to the proper one for the M601, and it seems to work (leaving the 2300 as the PPD file results in a warning and a failed print attempt).
 
I also tried printing something from a non-Adobe program using the M601, and there were two options available for printer quality (resolution?) settings.