A popular use for Tube Screamers historically is to turn the overdrive and tone to minimum and boost the level for a clean boost. Trouble with that approach is you had to make your mind up whether to use it for a clean boost OR as an overdrive (or just buy 2 pedals!). With the TS808DX on your board you get both in one pedal: the boost and the overdrive are completely independent of each other so you can engage the clean boost with or without the overdrive and vice versa. And as a neat touch you can choose whether the boost comes before or after the overdrive, which gives you the choice of driving the overdrive harder for more gain (in Pre mode) or making the overdrive louder (in Post mode) for solo passages where you need to be heard.

And now the geeky bit you've been waiting for: yes it does use the JRC4558D chip: the original, best and most sought after chip for Tube Screamers so you know you're getting THE Tube Screamer tone that has graced thousands of professional stages and studios.