Can I daisy-chain the PM-16 Personal Mixers?

Absolutely. There are two Ethercon/RJ45 jacks on the back of the PM-16. They're labeled "in" and "out". Simply connect an RJ45 or Ethercon connector to the "in" to supply signal and power to the first PM-16. Then, connect another one to the "out" to provide signal to the daisy-chained mixer. Power for the second mixer won't pass through, so you'll need to use a local power supply for it, and each additional mixer down the line. The Elite Core PM-16PS is the power supply you'll need, and it's readily available as an accessory for your PM-16.