Oh I'd go better than the E10K if possible. That's pretty much lower end entry level and the HD 600 much like the HD 650, scales quite well with better equipment.
You could go with a computer soundcard with a headphone amp. That's where I started with an Asus Xonar STX ( discontinued and replaced with the STX II ). This is a good option if you also plan to play games and need virtual surround modes. Prices range from about $50 up to around $250 depending on the amp/DAC and features the card has.
Entry level discreet devices would include the above mentioned Fiio E10K and the Schiit Fulla 2. Both are amps with included DACs.
Moving up to what I would consider 'audiophile' entry level would be where I'd recommend starting for a...