I can't comment on the SSl because I haven't used it.
I am a Tonelux owner. I have a mixer / summing rig, with 2 TXC compressors. Although it's not inexpensive, in comparison to a large format desk, it's a great way to get your foot in the door. You can always expand the system to lots of channels, eq, busing, compressors, and finally to a full on console.
As far as the sound goes. I always felt there was something odd about the high end when mixing ITB. The TL system cures the shredding weird high end for me. There is something really pleasant sounding overall, even when mixing heavy rock records. The Mix Bus has lots of gooo and depth without losing the punch and clarity, and with tons of headroom. I have one VRack of modules. It's small, but when you pick it up, it's got the weight and feel of really well made gear. You get what you pay for with this company.