The STX-22 is a monotube damper the relies mostly on the main piston shimstack arrangement to control damping. This allows you to potentially run digressive or regressive damping tunes, something that can’t be done without modification on a shock like the X2 that uses a ported damper design. On the downside, Ohlins and Fox seem to think that monotubes can cavitate more easily and react slower. Others argue that monotubes don’t heat up as easily, something to consider when the oil is insulated by an air spring.
The coil TTX-22 however, is really interesting – as it is a twintube recirculating design that relies heavily on the main piston shimstacks unlike the Fox DHX2 and Float X2. This means you have all the benefits of the twintube design, but have a shock that can be pulled apart and have the damping characteristics tuned to be digressive or progressive. The fact that it has midstroke shims as well, means that there damping transition between low and high speed is supposedly more controlled on the Ohlins TTX-22 design than on the X2. However, Avalanche suspension and I think a few others have modified the X2 with main piston/mid-valve shimstacks.
The main benefit of the Fox X2 vs the Ohlins TTX is that the former has a wider range of settings, due to being a ported design – and is thus easier to mass produce and sell after market.
