Steven doesn't appear to be actively advertising the Zbit. I'm not sure why. I stumbled upon it from his post about why many of his smaller amps don't have balanced inputs.
If you read my posts on the Zbit, you will note I mentioned that I felt the sound of the Zbit directly into the Taboo III resulted in a slightly more detailed sound. So, yes, IMO, the Zbit is going to provide a slight improvement over using a CSP3 at about half the cost of the CSP3. When I spoke to Steve about it, he agreed with my assessment and said that he uses the Zbit the same way. That's not to say that the CSP3 doesn't offer other benefits, but it is one more device in the audio chain. Simpler is often better. If I hadn't already owned the CSP3 and didn't need a preamp, I would be very happy to go with the Zbit and Taboo III. Also, if you need more inputs/outputs you could always get Steve's ZSB (Zen Switching Box). I'm not familiar with the Parasound Zdac you have, but according to Steve, if the DAC has TRUE balanced circuitry (not all do), the Zbit should provide a sonic improvement.
About the resistors, all you need are two 8 ohm resistors ( I used two: Mills MRA12 8 ohm 1% M1324). Each resistor has a fairly long bendable metal wire coming out of each end. For the left channel speaker output: place the wire end of one resistor into the minus (-) output terminal and the other wire end of that resistor into the plus (+) output terminal. Repeat for the right channel. Don't worry about orientation of the resistor between the plus and minus terminals. You could also mount the resistors on a dual banana jack to make it easier to add and remove. Of course, if you keep the speakers connected, you don't need the resistors at all. You don't have to do this, you can leave the resistors off and still enjoy the headphones.