Jack Dempsey companion question...

I have a 40 gal. tank in which the only current inhabitant is a male Jack
Dempsey(~5-6"). I had also had 2 bala sharks, 1 yellow lab. and a pleco in
there but during our last winter storm here in the NW, we were out of power
for 4 days and the only fish to make it out of my two tanks was the Jack.

I would like to get a fish or two in the tank with the Jack, but am at a
loss for what I should get. I thought of getting another one (maybe a
female) but the two LSF I've gone into both said not to get another Jack
Dempsey but perhaps another cichlid of equal size and temperament.

Most info I've seen on the internet says that Jack Dempsey's can be kept in
a "species" tank. Does that not mean with other Jacks?

I am also curious if there are any invertebrates (crabs especially) that
would do ok in there.

With only 3+ years under my belt with aquariums, I consider my self rather
new to it still and would appreciate any advice at all.

Thanks,
Tommy