I had the thought that before I purchased the K3 second receiver, I would experiment with SO2R using the K3 and the K2. I use WinTest contesting software and this has a dual logging/sending facility (SO2R) that allows 2 rigs to be connected. I had been under the impression that you needed one of those fancy SO2R boxes to get started, but soon realised that there are many different levels of automation in SO2R, from none to completely automated.
The one prerequisit as far as I'm concerned is to be able to hear both radios through 1 set of headphones. I did this with the following bits I had around the shack:
2x stereo headphone jack to two mono sockets
2x mono to stereo adapter
1x 3 way 3 pole switch box
The radios in their current configuration basically output 2 mono channels each. One on the tip and one on the ring of the headphone socket. I used 2x stereo to two mono splitter leads (available from maplin) to allow various combinations of audio at the input of the switch box:
1) Rig 1 tip to headphone tip, rig 2 tip to headphone ring.
2) Rig 1 ring to headphone tip and ring (using mono to stereo adapter).
3) Rig 2 ring to headphone tip and ring (using mono to stereo adapter).
With the headphone plugged into the output of the switch box, I can now select from the above combinations to hear the K3 in my left ear and the K2 in my right ear or the K3 in both ears or the K2 in both ears. I was worried about mixing the earth connections from the headphone sockets of both rigs but in practice this seemed to work fine.
To help prevent interaction between the radios when transmitting from one, I have cut 2x 23' coaxial stubs (one shorted and one open circuit). I have assigned the K3 to operate on 40/15m and the K2 to operate on 20/10m. A tee piece spur from the coaxial line from each rig provides the connection point for each stub. The shorted stub is connected to the k3 coax as it filters 20/10m and passes 40/15m. The open stub is connected to the K2 coax and it filters 40/15m and passes 20/10m. This will hopefully allow me to simultaneously run on one radio and S&P on the other without too much interference.