I attended one of these concerts, and it was a fine performance indeed. Orchestral execution was at the top level, though some of us will quibble at the shy tamtam at the end of the first movement.
At the concert, the MSO was giving away CDs of all the Brahms symphonies, also excellent performances in very good SQ.
For capturing audio, I use Audacity. I'm usually running Linux, but Windows and Mac OS (10.6 and later) flavors are available too. SQ will often take a hit through online sources, and the MSO offers good-sounding MP3s of M6 and M7 (Delfs) for $4.99 each.