Barry,
Both 00:16:41 and 00:1A:6B are reserved is USI (USinternetworking?) - [Link: coffer.com]
As I seen, when Pronto works with extender(s) in standalone mode, it connects to Ad Hoc WiFi network (Pronto_Network_1 etc or Marantz_Network_1(?)), assigns an automatic private ip 169.254.xxx.xxx, and sends the broadcast packets with http(!) data like "Hey, I'm TSU9600 with MAC=XX:XX:XX:XX:XX:XX and IP=xxx.xxx.xxx.xxx, is there an extender with ID=x?". The rest of this fascinated dialogue was left from my Microsoft Network Monitor, due to it was not broadcasted. But it is enough for me: this packet means that Pronto has no extender's IP at this moment, and I can't assume standalone extender by IP at Marantz Wizz.It Ex.
I think, the MACs of Marantz are the same, and only "Philips" and "Pronto" are changed everywhere for incompatibility purposes.
I'm so sorry for invisibility: both my bad practice in English and time devouring crisis moves me off the posts, but I'm trying to track the themes.
Currently I'm working with Crestron, and there are a lot of projects when I use Pronto as remote for Crestron's control processors, and I can only dream for conciliatory research of new control solutions somewhere in warm and sunny paradise, say FL or HI...

Lyndel,
I was surprised with ProntoNIC, thank you! For a year ago I was asked ProntoTeam for protocol Pronto<->extender, due to I was an idea to use RFX9600 as an endpoint control solution at the amount of remote offices in a huge video conference system with Crestron control logic. ProntoNIC looks really helpful for this purpose due to Philips themselves is yet not ready for these integration ambitions.