No, you don't need 500W in 4 ohms. That's nice to have of course, to crank that Tron soundtrack at 105dB. I have played that same soundtrack in our big, big room, and the D'Agostino Momentum M400 barely go past the 400W mark. And that's at absurdly crazy loud levels.
So, no, for usual volumes levels, you need half of that.
I would love to listen to the Lamms on YG. Like Keith found out, it's not all about QUANTITY, but QUALITY, and I think the Lamm would deliver that. A certain well known brand that he tried, with lots of power on tap, came dead last. It wasn't for lack of power, but simply the QUALITY just wasn't there (like I told him it wouldn't be).
I'm glad Keith took the plunge on a different preamp, after much suggesting on my part. The problem there was that he DID have a great preamp (in the Music First), but it was just not what his system needed at that point. I remembered Keith likes tubes, and at that point, he had none, so, enter the tube preamp!
Personally that's where I like some tubes in a system as well, in the preamp, and again, I'm glad he found a piece that works for him and complements the Ampzilla well.