The 234 and 424mkII sound very much the same.
I've not compared the specs on each of those units to the other, but I'd say they're probably virtually the same specs. Any differences in specs would be minimal, if any, but it's probably worth checking, nonetheless.
However, the 234 has a sound quality that seems very slightly better than the 424mkII. Although there's a subjective judgment to any "sound quality", I'd attribute any real differences in sound to be due to the 234's higher quality grade of components, versus the newer 424mkII, which was produced when "cheap" was a design goal that competed with "top quality".
With that being said, both the 234 and 424mkII should have roughly the same sound quality potential, with differences so minimal as to be insignificant,... where the real variance in sound quality depends on the engineer and technique.
If I were to make a quick snap-judgment about the 424mkII and 234, I'd say the 234's sound is ever so slightly better than the 424mkII, but you're then down to splitting hairs on the issue.
Some of the sound potential & resulting sound quality of a recording setup is dictated by type and quality of features,... which almost goes without saying.
/DA