I don't have an account at TWC, but regarding Salm it is the name of an eponymous mythological/epic founder (already it could be an anachronistic later projection in the past) and must be remembered to be written in a South-Western Iranian language of the 10th century CE. Moreover iirc it had more to do with the hero's character, so it could've been "altered" to fit its perceived meaning at the time of the Shahnameh's composition.
While the region mentioned in the Avesta, Sairima, has been interpreted in various manners. I remember one being simply a geographical term for a land next to a river. Another that it reflects a simple Avestan plural noun, meaning Sarmatians. This opens the question whether the name was preserved in the oral tradition, making it very old, or if it had more to do with the geo-political map at the time of the Avestan fixation in its earliest written form...
Nevertheless, one has to bear in mind that nomeclature by foreigners in ancient times, wasn't usually done out of pure fantasy. It was actually an effort by speakers of a different language to render, in their own tongue, what they heard saying from local native speakers. In other cases we have pejorative terms, with a rather transparent etymology, for example Chinese sources calling nomadic tribes something like "annoying bugs" or "rebellious slaves".
In our case we are also lucky, because in the Northern Pontic region must've lived bilinguists, facilitating commerce, who knew both Greek and a North-Eastern Iranian language of the Scytho-Sarmatian/Sakan family (call it what you will).
Sauromatae has been interpreted as sau-roma-t-ae, or black-fur-plural-nominative. Bearing the meaning of "The black cloaks". This etymology seems to be corroborated by the Hellenic ethnonym employed by Herodotos to describe a group/tribe living beyond Skythia: the Melanchlainai, or "The black cloaks". It does look like this name had been reported to him by someone fluent in both languages and directly translated it to his Hellenic interlocutor.
Also this meaning was not lost to the locals themselves, there are inscriptions from Olbia and the later Bosporan Kingdom, reporting of Saudarates, the wearer of black, and Sauromakes, two kings calling themselves, in an Hellenised form, by the same concept. Georgian Chronicles from late Antiquity speak as well of Sawarmag/Saumarg, a king having a Sarmatian mother probably calling himself the black hand/arm. What I'm saying is that the locals themselves and their neighbours used that very word to describe these groupings.
All of this actually speaks for Hellenic proficiency in transcripting foreign names, Pseudo-Skylax's Syrmatae was probably a pretty good attempt at rendering the native schwa and syncopation.
If you want to compare more on this, Nart Sagas have preserved a social distinction having to do with wearing black, signaling out that particular character as a violent/crude/warring individual...
There obviously existed also several tribal endonyms and who knows how many more ethnogenetical self-designations, but historically it appears that during our time, these particular steppe nomads came to distinguish the arms-bearing freemen as black mantles, possibly a garment which signified reaching manhood and social prominence.