There is an other way to tether your K5. It is by Eye-Fi Pro X2 8GB SD card. This is no real tethering, in the pure sense, but by this you just send the pictures, wether it be JPEG or RAW/DNG, directly to your computer.
I use it on my MacBook and it works fairly well. just observe some rather strange roles: never put the laptop on the left side of the camera (seen from behind) the metal shell of the body (this is a Pantax advantage, really) is somewhat stopping the WIFI's radio waves (this is what I think). On the right side, where the plastic SD card door is, there the waves can get by. Never set it up further than a few meters and a little behind the camera. Then, perhaps, you can have the pictures downloading in the LR3's watch folder.
Do closely observe the suggestions made on the Eye-Fi's website and their help desk is very cooperative too!
I was a little surprised seeing the RAW files coming in faster than expected...
BTW, after years of professionally shooting digital Pentaxes, I did not run into serious limitations, even with heavy studio flash generators and handheld bare bulb flash torches...
The only limitation is my imagination, sadly enough!