Amen to that.
The Creek OBH-21SE is an excellent small headphone amp, and works well with Sennheiser 600 or 650 headphones, which I think are among the best available for combination of sound and comfort.
The portable unit that comes immediately to mind is the Hi-fi Man HM-801, which handles FLAC. As an added bonus, it also is a DAC with USB and Mini-coax inputs. You can read about it in great detail at audioadvisor.com.
Others will undoubtedly provide excellent alternatives.