I have the ELK930 Doorbell Detector and have one tip for you.
My Powerflash is set to Input B and Mode 3. That gives you a dry contact closure trigger and an X10 On when closed and an X10 Off when opened.
Is there any AC outlets fairly close to the transformer; where the ELK930 would go? I have maybe 30 feet of #22-2 wire between my ELK930 Output and the Powerflash Input. That is in a close outlet to the transformer position.
The ELK930 has a solid state output and is polarity sensitive.
Connect the Out terminal of the ELK930 to the Negative input of the Powerflash.
Connect the Neg terminal of the ELK930 to the Positive input of the Powerflash.
OK for those thinking Brian H you reversed the polarity. Well Input B the Powerflash generates a small trigger voltage and it is reverse of the markings on the case. Positive is on the terminal marked negative and negative on the terminal marked positive.

The plus and negative markings are for when a DC voltage is used to trigger it in Input A mode.
As mentioned. You could also wire the Powerflash Inputs across the bell and use Input A Low Voltage Trigger; if the bell is 18 volts or less. Wiring would not be the way Smarthome shows; as it uses the ELK930. Direct input voltage would not need the ELK930 at all. So if you can get the voltage that rings the bell to the Powerflash. It can be triggered directly and the ELK930 would not be needed.
The X10 PF284 and the X10Pro PSC01 are the same module. Some vendors sell the X10 and some the X10Pro.
http://www.x10pro.com/ In the Installation Manuals Tab you can find the PSC01.
http://www.elkproducts.com/products/elk-930.htmhttp://www.elkproducts.com/pdf/930-instructions.pdfAs you can see from the ELK930 manual. It is three small PC Boards that can be split from each other. You get two bell detector boards and telephone ringing detector board. I was thinking of using my phone one and a Powerflash to trigger a X10 Chime Module.