Hi Dale,
The Echo cards are in principal very well supported in Linux, as Echo actively support development of drivers.
They're even nice enough to post sources to a sample driver on thier site.
I've got an Indigo DJ here (that's 2 stereo outputs, one headphones level w vol control, the other line). If you don't need inputs perhaps that's a good choice? As far as support goes, assuming your PCMCIA slot is good, it works *extremely* well. I'm running 5 ms with it, on a moderate laptop and assuming your JACK graph isn't too heavy it won't xrun at all. Very happy with it.
Slight drawback is that one needs the "echomixer" (part of alsa) to control the volume, as it provides 8 virtual outputs. But the echomixer is a good tool, and if you don't need to reconfigure it, it keeps its settings from last use.
I picked mine up 2nd hand for a great price, perhaps worth checking out the 2nd hand market?
My advice: buy it. They're great :) -Harry