Tube headphone amp?

Earmax Pro is an excellent amp. I have one and cannot recommend it enough.

Mapletree Audiio Ear+ HD Super, particularly suited to Grado, but also has a high impedance output.

Bottlehead's Crack OTL Headphone Amp Kit is getting rave reviews by owners. Check out the Crack forum for more information.

Some folks were talking about flavor of the month amps on some other thread, I think that phrase applies to headphone amp even more.

Check out Head-Fi.org for more information on headphone amps as there are 50x more options when it comes to headphones amps as compared to speaker amps. I am sure there is a specific thread there on amps for Grado 80.

Last time I checked, some amps offered these days are in the over US$10k range! And the street is flooded with amps from other countries like China, Japan, Taiwan, etc. You can buy some of these on eBay too.

My advice would be to find out when the next local head-fier meet is and bring your headphone to the meet. Audition various amps that people bring, and see which one suites your taste. Most people there have more than 1 amp, and typically you will get to try out some of these more popular choices that people talk about.

FrankC