With the XA30.5s ability to deliver current and the sensitivity of your speakers, I would think the 30 watts would be more than enough for most listeners in most rooms. As Tvad says, it plays a lot louder and more robustly than its wattage specs would suggest (I think it is very conservatively rated). The extra 30 watts of the XA60.5 are really marginally more power in terms of loudness. And I'm firmly in the camp that less power will sound better if it is enough power to drive your speakers to the volume levels you require. I was using the XA30.5 with my 89db Merlins and power was NEVER an issue. With your speakers and 4ohm impedance, I would not expect power to be an issue for you either. Now you may hear from those that say you can never have enough power.... Ask ML what they think and ask Pass what they think. Can't speak for ML, but I've never known Pass to not offer good, honest advice, even if they prefer to sell you two amps instead of one.
