It appears as if the 6100 will decode the HDMI audio on it's own. HDMI repeater. So yes, it is better.
It really depends on your intentions here.
If you are looking to purchase an HTIB and stand pat with it, I'd say go with the 6100.
If your intention is to slowly build a better system over time, either go with the 5100 and build on to it, possibly with better speakers or a better receiver or start with a higher end year old receiver, one with HD decoding and get a slightly better set of fronts, possibly a center, and use you existing Sony's as surrounds.