K2S9800SE with Yamamoto A-08S, Good match?

Yes but you might loss bass drive.I would say a 300b SET or 845 might be best depends on room size listening levels etc.But if I could buy 1 new SET it would be the yamamoto. I have used many 45 SETs with horns like in link http://steinman.mesls.org/stereo/J%20Kalinoski%20Loudspeakers%20101.jpg pretty big horns 106db 4ohm system if placed end to end is 19ft across.Had to biamp with larger amp on bass horns. But my 45 SET amps easly drove the 10 horns total to great levels.

Friend

If the Yamamoto is a 45 based amp (1.5 to 2 watts output) it will drive the JBL K2S - but not with authority. The K2S is 8 Ohm, 400 watt max, 45Hz to 50Khz, and 94 db sensitivity. I currently use a homemade 71A amplifier at 1 watt max output on modified Klipsch 3.2 horn-loaded speakers (93db sensitivity). While I enjoy the gorgeous detail - I am hungry for some authority. Therefore, my next project may be a 300B homemade amplifier.

The VTL line of amplifiers will drive the K2S with authority, but when you move to pentode amplifiers - you loose some of that "realism" that triodes bring to the table.

Visit www.davidberning.com and check out the Siegfried 811 amplifier. The 811A triode is the best big triode that I have ever heard! Hope this helps.

Studio1

Thank you for the advise. I just got the S400 and will give a try later today. Also, I'll take a look of the Siegfried 811 amp.
Thanks
Stephen