Yep the Sabaj is very good for the money well worth a go.I bought one of these new on recommendation from fellow Wammers and I think it's excellent
Sabaj Tube amp
Yes mate, I was super surprised at the grip that wee amp had with the 400S. It was then mediocre with a couple of other headphones.^ The FiiO E12 is even better imo.
If you are OK with mains powered I can also strongly recommend a SMSL sAp ii.
They are both powerful with excellent grip and control, which is what the Deva and Sundara need imo.
Both can sometimes be found for around £50 or less.