I'm in the process of buying a Denon AVR-5803 receiver that includes Dolby Headphone capability and a pair of Sennheiser HD600 headphones and am wondering if I'll need a separate headphone amp to get great sound out of this setup. If people who own the HD600s and a headphone amp of reasonable cost (say under $350) can comment on recommendations and where to get the best price (e.g., online retailer) for the headphone amp if it's believed I would greatly benefit from one with the AVR-5803, I'd love to hear about it. Also, I'm going to need a 25' cord for the headphones (I have a LARGE living room). From what I've read, the cord included with the HD600 is pretty flimsy and since I need a longer run I'm thinking replace the whole thing with one long 25' cable. If anyone can make recommendations on make/model and where to buy (e.g., online) a good quality 25' headphone cable that will work with the Sennheiser HD600s, I'd appreciate that info as well. Thanks in advance!