You didn't say whether you were going to buy new or used. I have the older Lambda Professional and Lambda Signature earspeakers and SRM-1/MK-2 and SRM-T1 headphone amps. I recommend the Signatures (or equivalent in the current Stax line) because the bass response is far superior to the Professionals. The amps are in different systems, and I have never done an a/b comparison. Both sound good.
I haven't heard the Koss headphones. I agree with Sdcampbell that the Sennheiser HD600's are excellent for the price, but the Signatures are better.
I haven't heard the Koss headphones. I agree with Sdcampbell that the Sennheiser HD600's are excellent for the price, but the Signatures are better.