HI! I had one for years, I tried lots of fish with mine. A giant Gourami lasted the longest, (about 3 days) I had to seperate them because of damage to the gourami...
Maybe more big fish would have been key, as to distribute agressions.
Also, I only had a 75 gallon tank for them both. it was just too small anyways, and bad fishkeeping on my part.
I think if you buy one small enough and raise it with various other rough fish the Dovii could learn to respect territories and coexist?? maybe?
I saw a pic somewhere where they had one with giant catfish.
Good luck! I hope you get a better and more informative reply than my ramblings. lol!