IMF does stand for I. M. Fried, and the TLS 50 and the Qs are both related to him, but TLS 50s were british and the Qs american. Fried was a hifi dealer (Center City Lectronics) in Philadelphia in the late 50s and early 60s. Amoung other things, he introduced the Decca cartridges and the Quad ESL to the US, but eventually got invovled with John Wright and transmission lines and became the foremost apostle of TLs in the US. I think as the US distributor he suggested the name since it might help with sales in the US, which was a pretty important concern for the British then (and now). I think that Bud Fried had a lot of input into IMF designs, but Wright was really the head of the concern. In the mid seventies IMF and Fried went seperate ways -- I can't remember if IMF was bought by a swimming pool chemical company(!) and then went under (come to think of it, that's a joke) and then Fried started his own company, or whether he started his own company, and IMF, having lost its US distributor was weak enough to be taken over by the chemical company. But after IMF went bust, Wright popped up in TDL, which made similar TL speakers, and did well for a good long while, but seems to have also fallen by the wayside (perhaps a result of the death of Wright).
Fried, on the other hand, started making resistive line tunnel speakers, a simplification of transmission lines, which allowed smaller, lighter and much simpler boxes and stuffing. They were, and are, fine speakers, probably not the equal of full TLs, but much cheaper for relatively comparable levels of performance. The Q was either the first or one of the first of these designs and was a great speaker for its size and price. I bought a very early pair, but eventually replaced them with a pair of TLS 50s, which were superior in many ways, but didn't have the grunt that I always secretly wanted -- just not really great for rock.
I own a pair of Betas now, which I use in the kitchen, and am often surprised at how big they sound.
Incidentally, Fried was one of the few designers who understood series crossovers, and so if you try to figure out one of his crossovers, it may not make any sense if you assume its a parallel crossover.