Best answer by ratty
On the physical differences:
PLAY:5 Gen1: 5 drivers (1 woofers, 2 mid, 2 tweeters), in a rear-ported reflex configuration. It can only be oriented horizontally. Line-In and headphones jacks.
PLAY:5 Gen2: 6 drivers (3 mid/woofers, 3 tweeters in an array), in a sealed enclosure. Touchpad controls. Can be oriented horizontally or vertically. Line-In jack only.
As already noted the Gen2 is also dual-band, so can be used as surrounds with a PLAYBAR.
Acoustically they're quite different, even allowing for Trueplay room correction. The Gen2 is much more accurate, with more extended bass. It can benefit from a SUB, but does very well on its own.