Headphone Amp vs. Receiver/PrePro w/ Dolby Headphone for movies

[bilboa]

I am wondering whether a headphone amp will sound different than a Dolby Headphone output from a receiver or Pre/Pro.

I am looking at getting the NAIM Headline 2 AMP.
Also, any advice on whether to get the ISupply or the PSC-2 power supply.

I would be pairing it with HD650s.

thanks