The Rockbox currently works in read-only mode, so it cannot save the settings yet (work in progress).
Probably the most convinient way to save the settings is to grab a simulator, tune it up and export it via Settings > Manage settings > Save .cfg file, replacing the one on your Clip with it.
There are no Clip+ simulator there yet (although you can build one yourself), but the cfg settings are identical to Clip so far.
The stereo width should work, try to play with it more. The Crossfeed (L/R speakers microdelay effect) is good too, but I’m not sure if it’s supported on Clip (can’t test, mine is just being shipped). It adds a very natural sounding effect, especially on older-style hard-pinned media).
I think with the Rockbox soundstage tweaks & better headphones you might want to keep you Clip.
P.S. As it was pointed out, I recommeded only in-ear monitors and forgot to mention earbuds. The $80 Yuin Pk2 is imho probably the best choice in this category. They look rather inexpensive, but sound twice their price.
I know the prices look big, but it is better to to spend a bit more and enjoy the sound than save and torture own brain. Plus, they do last longer, so with the right “expensive” phones you will actually save on a long run. I personally use Westone UM1, (for comfort, I need to wear the phones all day long), and the build quality is unbelievable — the cord still survives the abuse that would kill a dosen of $25 phones already. They use some sort of special kevlar-like coating for cord and rock-hard plastic for shells.
I recommed you visiting a local shop to check the sound & fit, and lurking around head-fi for reviews & deals.