It sounds like your PK damper may be acting up, and no longer providing good ink flow. The solution would be to replace the ink supply system (which includes the damper unit), but if you feel the MK and all other channels work well, and you prefer printing on glossy media, then you could get a Pro Gloss only setup, and install the PK ink in your MK channel, and leave your printer in MK mode. Knowing that your printer is 5 yrs old and having issues with one damper, I will warn you that it may start having other issues in the near future, and flushing then charging with Pro inks could cause flow issues if your dampers or other parts are nearing the end of their life. Have you ever followed our instructions for manually cleaning your printer's internal components, such as the capping station, wiper blade + bottom of the print head?
Piezography Pro has a very warm tone ink set, that is similar though not exactly the same as Carbon K7.
You will need cartridges installed in all 9 channels of your printer, and refill carts come with reset chips attached (you just need to add OEM chips).
The Piezography pro ink set consists of a set of three warm and three cool tone inks, along with black (photo black, in your case) and Gloss Overprint. You get a warm tone print by using the curve blending sliders in QuadTone RIP, by using all or mostly the warm tone curve.
For Mac, you will need to purchase/download/install both QuadTone RIP and QTR Print Tool from www.quadtonerip.com
If you were impressed with your Piezography output on an 1160 (12+ years ago?), then you will be amazed by the quality and capabilities of Pro!
Please let me know if you have further questions, or there's anything else I can help you with.