Question:  We purchased a HME DX300ES system and I was wondering if there was an easy way to connect it to our theater's existing Clear-Com MS-702 party-line main station.  I know the BS-300 wireless base station has AUX in and out connections and was hoping there was an easy way to connect it to our wired system.
Answer:  The BS-300 wireless base station supports two 4-wire connections which support Matrix type intercom systems.  The MS-702 party-line system is an unbalanced 2-wire DC powered intercom system, so in order to make a connection to this type of system we will need to introduce a 2-wire to 4-wire interface, Clear-Com has several interfaces that can support this, they are the IF4W4 which can support up to (4) 2-wire to 4-wire conversions and the EF-701M which supports a single 2-wire to 4-wire conversion. 
In a pinch one could also use two spare single channel RS-601 or RS-501 party-line beltpacks to make the conversion, the 4-wire auxiliary connection from the BS-300 base are routed to the beltpack headset jack and the 3-pin XLR feed is routed to a channel on the MS-702 base station. 
See the diagram below for details on the system setup.