Juan,
You have great taste if fish my friend!!!
Let me see if I can help you here...................
1. H. carpintis "Escondido". I have these in stock. Beautiful fish, even more so then the standard carpintis....BUT IMO would kill your JD in short order.
The ones I have are very mean even at their current size of 2"!!!
2. Nandopsi beani...........another beautiful species!! Good luck finding it!! You need to take a number behind the 1000's of people looking for this fish. They seem to have vanished off the face off the earth.
If you know of some...PLEASE let me know as I would love to bring a thousand of them in and retire after that!!
In regards to compatibility with your JD....would kill the JD quicker than the carpintis would!!
3. Amphilophus trimaculatus....quick answer here....not compatible!!! SORRY
4. Nandopsis tetracanthus......BINGO!!! Good choice to house with your jack. mildly aggressive should compliment your jack nicely. I also just brought in 50 of these fish.
Also keep in mind the other choices would be just to big when adults as well as the aggression factor for a 55 gallon tank.
Sorry I could not be more help in your choices, but really the other three are just to aggressive for a jack!!
I also just saw your jack is 7"....may have a hard time finding a suitable tankmate of equal or close size to your jack!!
CM