Bill and Bob; thanks for the responses!
I did download the Elf Guide from the Bag End site, but it was no help.
I got two S18E-C subs. I've been working with one in trying to get set up; and I did run signal to it when I bypassed the Elf and it did produce sound. So that did eliminate the subs as the problem.
The front panel controls were set at -1 for gain and +5 for threshold. Eventually I tried moving both gain and threshold through their ranges, but to no avail.
I've emailed the seller about the problem and he emailed back asking for the info on the adaptor he sent. The one spec that was out of line was that the M2's specs called for operating current of less than 100 mA, while the adaptor is rated at 200 mA. I sent this information to the seller and he emailed back that he's pretty sure that it is the adaptor that he has always used with the unit, that he pulled it out of his rack when he listed it for sale, and that it was indeed working when he did so. He said the he would check his warehouse on Monday, to make sure there is not another adaptor; and if there is not, he said I should send the M2 back to him and he will get it repaired.
So that's where I stand now. I figured that when the two of you saw my post, you would be able to spot anything I might have done incorrectly; and the seller said that my email indicated I had it setup correctly. I don't want to try any more experimenting at the moment, just in case the adaptor is mismatched. I guess I'm going to wait to see if the seller finds anything on Monday, and then I'll probably be sending the M2 back to him for repair.