Audio Challenge on Dedicated Micros DS2

[Nelboy 0]

Hello,
My home system uses a DM Digital Sprite 2 DVR for recording, which I currently have no intentions to replace as it's a decent unit which does everything I want it to at the moment.... However I am now looking to add in audio on the system.

As far as I can see from looking at the unit there are only 4 audio ports in the form of RCA sockets - 2 inputs for recording audio on camera 1 or camera 2, and 2 outputs with one being for an exterior speaker and the other for a speaker at the monitoring station. The unit specifications state a functionality for audio challenge, wereupon using a microphone at the monitoring station would output to the exterior speaker, and yet there doesn't seem to be any input port for such a microphone in the form of a 3.5mm jack or an RCA socket.......

So is it possible to attach a microphone to the DS2 system for audio challenge without having to connect the system with an ethernet cable? (I'm pretty sure all the LAN sockets on my wi-fi router are in use for system extenders and a networked printer).... Really I want to have this connected up within the current week.