Bands of brothers; This is the week when groups can say it's all relative.(Preview)

Byline: GREG HAYMES

It's the Battle of the Brothers tonight on the Capital Region concert scene!

In this corner, weighing in with a massive discography that stretches back to their 1971 eponymous album debut, the Doobie Brothers chug into the Saratoga Performing Arts Center at 7 tonight. The band has been in the recording studio recently, working with such producers as Ted Templeman and Bob Rock, but don't expect to hear much new stuff tonight. And don't expect to see Michael McDonald, either. But with founding guitarist-vocalists Pat Simmons and Tom Johnston leading the charge, you can bet that you'll hear plenty of early Doobies hits such as "Listen to the Music," "Long Train Runnin' " and "China Grove."

The number of actual …