The real question is what's your budget (if that's not too personal) and what exactly does your BF already have? Stax-009 headphones are $5,000 for example - but are supposed to be the best out there ATM. With the Stax you pretty much HAVE to buy a high-rent headphone amp as well (another $5,000).
The LCD-3's are more reasonable in comparison but still around $2,000. A good amp for that can be had for about another $500 - $1000.
A headphone amplifier is in order if he uses headphones regularly. But to give a good recommendation it's important to know all the headphones he has or plan to has in the near future.
I'm from the speaker world myself, but even my really really absurdly expensive (think car prices) speakers don't compare re: detail retrieval from a good pair of headphones with a dedicated headphone amplifier. With speakers there is definitely an upper limit where you have to change everything to get the last 1% - 5% of available performance - custom/additional power from a dedicated panel from the elec. company, custom built rooms, serious room treatments... a lot of that can be avoided with headphones. 
<- this is a lot better than the stock converter, the stock one dosen't have the cable so it applies pressure.
