What does moving from a 150 watt amp to a 400 watt amp get you?

Back pain

and an empty wallet.

I think you have an excellent amp and I'd leave it at that. 

You need a lot of power to significantly increase volume. Doubling the volume requires 10x the power. Without doing the math, volume wise you may gaine around 4 dB going from 150 to 400. ( 150 to 300 is 3 dB). 

But  you may need a lot of current, which your amps should have. 

Best,


Erik 

I’ve seen others say that these speakers need to be driven by 400 Watts to get them to sound their best.

If you really need 400 watts to make a speaker work, in a nutshell the efficiency of the speaker is borderline criminal. The reason why is simple- if you want an amp that really sounds like really real music, you can count on one hand the number of amps that make that kind of power as well. With almost any technology, the larger amps tend to be less musical. The reason is that First Watt you hear so much about- while that is a bit of a generalization, the fact is that many amps at lower power levels actually make a fair amount of distortion. So if you have a 400 watt amp as opposed to a 150 watt amp, that distortion level might be a bit more audible.

How this manifests is that you loose low level detail- and there is a tendency to turn it up to try to get more impact.

If you're not clipping your amp right now, I'd hang on to it!