Zymol waxes have a high concentration of oils, so adding Zaino on top of Zymol is not a very wise choice, as it just will "lay" on top of the Zymol and not add any benefit, but it's your money. I'd just keep adding Zymol each time until you feel the Zaino underneath may be starting to be compromised by the Zymol, as it can happen. Tuff as Zaino is, adding top coat of wax you run a risk of the wax oils/silicones trying to migrate to the finish. Not that it will happen, but it may. It's the oils that try to "eat" through Zaino.
For a bit more longevity in wax, try S100 or Souveran. Not that there is anything wrong with Zymol, just that due to the way Zymol is made, it has a tendency to wear off quicker than other waxes.
Hell, I still have Japon and Detail in my frig, but now use Souveran if and when I wax as opposed to Zaino sealant. I just find it (Zymol) costs a lot of money for a wax that does not last long, but it looks good due to the oils. Kind of like Megs #7, which has a good amount of oils. Here's a link on Megs #7 from Mike Phillips of Meguiars:
Megs #7
I'd just stay with Zymol upkeep for now. Leave the Zaino on the shelf until you need it, then strip the waX with one of two methods, a Dawn wash and or alcohol/distilled water spray & wipe. Then, add your ZFX/Z5 or ZFX/Z2, let it cure overnight or longer then put your Zymol on again.
As for QD, I still use Megs FI. It's cheaper than Z6 and I save the Z6 for further coats of Zaino, as I spray Z6 prior to and after each Zaino coat.
For Zymol, you could use the Field Glaze, but that too is expensive and find Megs FI does a very good job without added expence. Buy it by the gallon to save if you do a lot of QD'ing.
Again, I'd contact Sal Zaino on this matter as he can assist you in getting the best results from both Zaino and or Zymol without the waste.
Regards,
Deanski