a bit too much salt for a cichlid i suppose , but i did came across talapias and snakeheads in blackish water around 1.010 and talapia is a cicihlid...if im not wrong.
actually firemouths and other thorichthys come from the same areas as platys and other livebearers. therefore it may be entirely possible to keep firemouths and other Thorichthys with some salt. I surely wouldn't put them straight into a tank of 1.008. Instead I'd raise the SG very slowly. I'm not saying for certain that the firemouths will be able to tolerate the salt on a long term basis, but it may be more possible than one would think.