Why didn't you pick up the Asus Essence sound card instead? For an entry audiophile headphone such as your jvc, the Asus card would've driven it even better than the X-Fi IMO.
The Sennheiser HD600/650, Beyer DT880 and others are entry level ! The Grados G1000 and Sennheiser HD800 are for those who want that extra bit of detail.