Never owned one of those zero turns or even been on one.  However, you're going from a "premium" mower to a higher grade homeowner level mower.  To get equal quality you'd need to go up to the 900 series with the Kawasaki engine.  You also get the 7 iron deck, which is much higher quality.  No idea what motor is in the 540 but again, you had a serious mower and if you're like me you'll expect the same out of everything else.