Angels? festivum to me are basically just a severum and angel in one fish. in terms of looks and personality. You could try some of the smaller growing Geophagus species like Balzanii, I had one that never actually got over 4". he was actually in that same tank. I tell you what, my tank was bigger than 33, but I kept mostly smaller peaceful cichlids with community fish, so I will dig up some pictures for you. Obfiously not all fish will be suitable but at least it could give you some ideas!
thats, rotkeil severum, Gymnogeophagus Balzanii and a parrot cichlid
Boesmanni rainbow, Snakeskin gourami and Sorubim Lima catfish
my very grey rainbow cichlid
full tank shot, the plants were live and the severum never bothered them
As far as I remember I kept
Golden wonder panchax x3 (had a huge 4" female)
boesmanni rainbows
red tail black shark
blood parrot
rotkeil severum
Flowerhorn parrot ( I moved him eventually)
6 snakeskin gourami's
Rainbow cichlid
a few dwarf cichlids
It was a very cool tank lots of activity. Severum was very relaxed and never bothered anyone, same with the parrot. I hope I've given you some Ideas on what you could do. If you have any questions about certain fish you like and want to mix then just ask me because I know some good fits for your tank.
Bare in mind that angels need at least 30g tank so you could have some of them. An LFS near where I used to live had a huge community SA tank that had all kinds of tetras and small catfish in with dwarf cichlids and other peaceful fish like festivum and angels, dwarf cichlid species, keyholes, severums, more peaceful members of Thoricthys family (firemouths CAN work but you can get some really nasty ones too) I think there was some kissing gourami's in there too and they could live in your tank.
Unfortunately for you the dempsey will probably end up taking over the tank whatever you put in there so if you want a peaceful community tank of more than just one fish I suggest you return the dempsey as they only really play nice with large aggressive cichlid species.
make sure that you know things like severums take a long time to grow and if it did outgrow your tank or become a problem you always could rehome it, until that happens though the severum will not pose any threat to other fish.