Best Headphones in $500 range for Leben 300X

This won't be what you are expecting but that sounds like a perfect amp for some AKG K1000 earspeakers, which you would use not with the headphone input but with the speaker terminals. Originally they retailed for about $1000, but Headroom (headphone.com) took out the remaining stock from AKG at one point and sold them for about $500 so there should some people who sell them around that price. They don't come around much and on balance, when they do, they usually are a bit higher in price.

They need about 10W (because they are so insensitive) but I think they are wonderful. To me, they are the best headphones I have ever used/heard (I have heard a few generations of top Sennheisers, the Beyerdynamics, the Stax phones up to the top end, the top Grados, and others and I have never found a pair I'd rather have than the K1000s. They are not completely quiet for the person sitting next to you on the sofa (because they are more open than open-ear cans) but they are fine for 'apartment living.'

I second the AKG K1000's. They are the best headphones I've heard.

Michael

The AKG 1000 are spectacular. Apparently, everyone agrees.
There is a pair available in "New Today" for only $1200.
Is that inflation, or just supply and demand? You be the
judge.

Just after I posted, I looked and there was a pair for $950. Wonder if this new pair is coincidence... :^). While I think they are great, and I haven't followed recent used market prices, I think they can probably be had for less if you wait a bit.

If you're looking to use the headphone output rather than the speaker outputs, I can highly recommend the AKG K-702. They take some time to burn-in but when they do you are well rewarded with amazing transparency and neutrality. Bass is not as prominent as the Sennheiser 'phones but seems more real and less bloated.

My best advice would be to visit the Head-fi website and get some advice from people as hooked on headphones as most on this site are hooked on hi-fi!:-)