I back Tvad. A match between Power Amplifiers and Speakers is more important than Pre-amplifier. Everything depends on the type of load your speakers present to the Power Amplifier.
See the following article. This will give you the details:
http://www.symphonysound.com/articles/tubefriendly.html
See the following article. This will give you the details:
http://www.symphonysound.com/articles/tubefriendly.html