I make a huge bump on this topic because I just got myself a used THX 887 for 200€. I can compare it to my SMSL HO100.
My setup is as follow DX3 pro V2 (as dac) → RCA → monoprice → RCA (passthrough) → HO100
With that wiring, both amps are fed simultaneously with the same DAC.
I must say I’m quite happy with my purchase: the THX is flatter than the HO100, giving a better sense of space. So a 400€ amp of 2019 is still better than a 150€ amp of today 
there are 2 things that I notices though: dynamic range seems bigger with the HO100 (but it could be a byproduct of the FR), and if cymbals are less harsh on the THX, the “sh” and “ss” sounds can be way more sibilant. On the dynamic range subject, it can be a plus though, as the listening is easier.
So all in all, the THX887 is not quite a perfect amp yet; I hope using it balanced (in and out) will help with those defaults.
Edit: the controls feel way better on the HO100 (but it is subjective as I’m a sucker for those aviation style switches).