Not heard this combination, but can testify to the M1 sats abilities. Also, they are available as single speakers, so you don't have to worry about buying the complete MT-25 and flogging the 608 on.
My experience of the REL Quake is that a stack of weight on the top helps to tighten up the sound and make it a lot better for stereo. Not what you asked but might be useful!
All I can say is that for it's size it goes pretty low, but the speed and agility is stunning whether with music or cinema. I don't know the connections on the 608 but the REL can be connected via a neutrik speakon and a sub (phono) lead at the same time and uses both at the same time. I upgraded a Kef 5005 system (a while back) I had by replacing the large but very slow psw2500 sub with a Quake and the effect was instant and stunningly good.