Q1-Yup, crappy stock pads, Superlux pads are no go with sz2k, so I'm waiting for my 77x (have to import them too, not even shipped yet,duh)
Q2- Good question, searched for a while but there is no info about Clear Bass freqs :\ At least it is better with Clear Bass +3 Fiio boost +8 that Clear Bass +2 Fiio boost +10db
Don't stress on bass impact. Those pads are energy killers.
The 77 are a win/win. On their own they are beasts. 57mm and I modded mine and they are very very close to the sz2000 just in impact. Those xx pads will make a big difference on your head. Isolation isn't great but you really should go one step at a time. Find the hit. Enjoy it. Estimate how much you can sacrifice by getting other pads like HM5, Alpha's that give better isolation but sacrifice a tad bit of the hit.
Where is that Clear bass boost? The vibe...the high speed is the sub-bass. the flutter and lifting is upper bass hits.
I wouldn't spend another penny until slapping the xx pads and maybe isolating that Clear Bass's frequency tweak.