Well, since you're using a receiver, all you really need is a way to bypass your laptop's internal audio interfaces and implementations and have it simply off load out to something that can carry a virtually untouched signal to the receiver to have it process the signal with it's dac and output via it's amp to your headphones. The output impedance of the headphone jack on your receiver is likely high, as almost all are, so it would be best matched with a headphone of higher impedance as well. To bypass your laptop and output to your receiver, you could use a simple USB DAC or find something to allow optical output. The Muse USB DAC is an inexpensive way to do this. As is the Hifiman HM101.
Alternatively, you can stop using your receiver, and get a decent entry level USB DAC/AMP unit to bypass your laptop, and remove the need of using your receiver, and keep it simple and clean. A Fiio E10 would do this wonderfully. This also has line level output if you ever wished to output to your receiver still, or another amplifier, etc. Does what the above USB dac's do, but adds it's own little amplifier to the mix if you need it, but still allows you to output to other devices all the same. Highly recommended.
Lastly, if you really want to improve, get a better headphone. Set a budget, do research based on what your preferences are, and get something that will really dazzle your ears. A newer better headphone, within reason, is going to be your biggest upgrade at this point from your current MDR CD 550.