Hi. I've experimented with Bryce 5 to make the landscapes for FMS (It's perfect to create sky texture with it). The landscape format in FMS is very simple, and it is only bitmaps controlled by a "height bitmap". Not real modelled landscapes with 3D software.
What I've done is to create landscape texture with bryce, and render it from top. Then I split the rendered bmp into smaller pieces, and specify the position in the .scn file. I also take screenshot of the "height bitmap" (the greyscale topography map in bryce that defines the height of the mountains). Then I use this as the bitmap that makes the topography in the FMS landscape.
If the mountains seems too low in FMS, open the topography image in a photo editor.. and for example increase the contrast. Then the white parts get more white.. and the dark more dark... or remove the contrast if you want it more flat.
Take a look at landscape Rekvin18 on my site. It's a landscape made with help of Bryce (you find it under Landscapes G1).