DP1M: flash system compatibility

Hi everybody!

After the purchase of DP1M I’m looking for good flash for it and really hoped to use my old Metz 54MZ. The problem is that Sigma’s TTL flash system is not notified as compatible with Canon, Nikon or any other flash system widely used on the market. So my question:

- What is known about Sigma TTL compatibility with other flash systems?

- Which flashes you can recommend to DP1M other than only one official Sigma’s flash for this camera?