OK Chris & Bill, thanks so much! As Bill said, I'm really lucky to have access to this community.
To make a long story short on the jact1/jack2 issue, I could be wrong but I believe, based on what I've read and observe, that my AVL system is probably not corrupted, and is using jack2. I did searches thru install packages and saw nothing related to jack1 that got installed by mistake. The only jack processes I see running are qjackctl and jackdbus, and the jack_control commands work. I'll keep alert to any signs that my system somehow has both of them mixed up, but I don't think it does.
Last night I got it all working, basically following all the advice I've received in this thread. I have a jack_start.sh script which uses jack_control commands and has a patchbay profile to reconnect the objects. I have a simple 2-way crossover at 60hz, and it works. My piano app see's a 128 sample buffer, and I don't see any xruns. It sounds reasonably well. BUT.....
Maybe jack does not play well with ecasound, because the below-60hz channel seems way attenuated. Also, I seem to feel too much latency. I turned my woofer amp up all the way, and I can hear the bass OK, but this is just not right; turned up that high it should blow out the windows. Without the ecasound/Richard Taylor LR crossover, it has much higher SPL for same setting. (I learned about ecasound, and downloaded some ladspa filters, from Richard Taylor's DSP website.) I'm pretty sure that when I tested using just ecasound and not jack, I got plenty of volume out of my 12", large cabinet woofers.
So darn, now I'm not sure which direction to go to most efficiently solve this. I could start switching wires around to make sure it's not something about my hardware, etc. But my suspicion, based on what y'all told me above somewhere, is that ecasound and jack are not completely compatible in some way, and I need to switch to the zitaIrc packages... Or, I could stop using jack, study the Richard Taylor posts carefully, and see if there's a way to connect pianoteq to ecasound without jack, like with plain Linux pipes maybe. Thoughts??
Thanks,
John