Hi,
That's a pretty cool server -- topo lines from SRTM data, so for almost the whole world.
I used your string and am getting tiles, but also occasionally an error message. Do you get that too? Seems odd since it loads maps for a while, then decides it doesn't like the request string?
I have not yet added easier WMS support (layer picker, basically). I've just done a few things to make the request string handling a bit more robust.
Looking at the getcapabilities for that server I think you've got it. With the 10 meter first it should draw that, and then if that isn't available, go to the higher layers.
The server seems a little slow, but let me know what you think of it and if you keep seeing errors. I'll try it again later in case it's just a temporary hiccup.
Oh, and your question about transparent gif -- no unfortunately it doesn't work that way. Transparent will only function within a WMS server itself, so it's for combining maps on a single server. I do plan to implement combo mode for landsat (lat/lon projected) maps, and if this server turns out to be good, it would be good motivation.
Thanks for the post.