A good friend had a RTBS in a 6 ft tank... Don't know the volume..... But it had similar fish. I don't see a problem if the tank is over stocked. However, you would need to double check each fishes requirements and tempraments.
Some of those fish may prefer slightly alkaline water, where as the rams and emperors prefer slightly acid water.
With fish being raised in tanks this may not be critical so check it out carefully first.