yup. SQ is sound quality. usually defined as a fast sub, responsive, tonally accurate, and with good detail and clarity.
SPL is sound pressure level. high excursion SPL subs are designed for competition events where the loudest car is essentially the winner. for an example of an SPL sub, go to www.reaudio.com then go to products, subs, "MT" line
The Brahma has excellent sound quality at higher levels, I feel better than the Shiva. Credit that to it's linearity and motor strength due to the suspension and the XBL^2 motor design. It has a very wide BL curve, and keeps its composure at high volumes.