A dedicated headphone amp certainly isn't essential.
The headphones sound excellent through the headphone out of a CD player, and even very good just through the bogstandard 3.5mm jack on my laptop. So even if you weren't happy at work, you wouldn't need to spend much over £50 to add a soundcard to do the trick.
They are readily available: Superfi definitely used to sell them, as did Richer Sounds. All good DJ shops will carry them. Digital Village (
www.digitalvillage.co.uk) is a reputable shop, with real branches, good service, and fair prices, and you can order online. I don't think any of these will take them back if youre unhappy, so as always I recommend an audition first unless you have money to burn. I don't think youll be disappointed though...
Just had another thought - if you listen for hours at a time, these 'phones will probably get very uncomfortable. simply because they rest on the ear itself. sennheiser do some new, similar models which go around the ear - look at their website under commercial headphones, these may be better for you, but im making no promises about their sound