250 ohms is pretty high in terms of impedance for headphones, but there are higher. High-quality Sennheisers are 300 ohm, but some Beyers are 600. You need high gain for headphones such as this. You're not going to hear the noise floor of the amp when using higher gains in situations such as this because the impedance of the load (the headphones) means the amp is following a different performance curve. (That's why they test amps at different load impedances.)
As for Foobar, I've used it for years in all sorts of devices and venues. I stay away from the WASAPI/ASIO stuff - makes things too dicey, depending on the hardware and rips as some have commented. IMHO, the best thing you can do is make sure you always have the latest Foobar revisions, then add more codecs such as Monkey Audio, etc. Definitely download the LAME FLAC decoder and set it up so that Foobar can use it. Stick with FLAC if you want the best sound quality. Rip your CD's using EAC (Exact Audio Copy) and then use Foobar + Lame to convert the wav files to FLAC. Keep the Monkey Audio decoder if you download instead of/in addition to ripping from CD's.