lossless

Specifically looking at the Harry Potter blurays, the first 5 films have a 5.1 LPCM track at a fixed 5.8Mbps, but the last 3 films have either a TrueHD or DTS-HD MA track. Having just finished the 5th film and starting the 6th, I've been astonished by the increase in surround and LFE activity...

Is there a noticeable difference between 5.1 and 7.1? Are movies exceedingly immersive with 7.1 versus 5.1? I have a 5.1 Onkyo that decodes lossless and I'm already blown away so is it worth the jump in price for 2 more surrounds?