Technical question on phase inversion.

This past weekend, I replaced my solid state preamplifier with a tube preamp. What a difference! I really like the change in the sound but I'm confused by one thing. The MFA Magus B manual says this about the main outputs,  "NOTICE: The high-level stage of the Magus preamplifier is an inverting amplifier. Many audiophiles prefer to correct for this by reversing the speaker cables on BOTH speakers (+ to - and - to +)." So, now I'm confused! I have tried it both ways and they both sound good to me. I'm wondering if there is a rule of thumb about "inversion" that I'm not aware of. So far, I'm only listening to CD, if that helps. Don't get me started on how to correct for inversion when playing analog. That's my next adventure!