The 828's technology is friggin ancient and quite dark and blurry, so the difference you're hearing is normal. Put a test tone on in your DAW and sweep down into the sub frequencies to see if the card is reproducing them correctly. If it is, my hunch would be that its giving you a tighter bass, and the reduced booming is tripping you out a bit... you'll get used to it
And just in case, the brightness you hear is in the FF models as well... Im pretty sure all RME cards have that topend - personally liked it, made everything sound chique.