Weird.... I have 2 of these within my house and they happily coexist no problem.
The HDS-600RS is different to a Slingbox in how the ports work. By default it will appear to assign itself with 5101 (not the Slingbox default of 5001) and then work it's way up the number chain if another device using this port. You can't appear to manually set a port number but you can specify network IP stuff.
Shame the installer gave up. Why not give the SlingLoaded team a call? I am sure they will be able to help.