how much power

Roxito, good thread. I am currently researching the same scenario with my bedroom system, which consists of a Yamaha RX-V1800 receiver driving a set of Monitor Audio Silver 9i towers. The bedroom is the master, and not small, at 14 by 16 feet. I think the speakers are rated 6 ohm, but may drop lower than that. The 1800 is rated at 130wpc into two channels. But it seems that if I crank the volume even to what I would consider a moderate level, the sound gets "glassy", loses clarity, and generally gets somewhat unpleasant to listen to. Could be increased room reflections, but I think there is more to it than that. Could also be speaker cables, which are Goertz MI-2 Veracity.

Magfan,
I'm with you, just didn't want to get into all the advantages of Magnepans and answer the OP's question as to why "he" "may" need more than 50 watts. If I listened to the Left Brain crowd, I would have never tried a Cary 805 (50/70 watt SET) on my Maggies. That would have been a loss.

No problemo. I used a Kenwood integrated for a while...with MG-1s. This was quite a while ago.

As to 150 watts and 45 amps? That's about 3.3 volts. Clearly something doesn't add up.
My panels are fused at 4 amps for mid/tweet. Figure 8 amps full tilt for the whole enchilada. Why would I need 45 amps? My Ice amps have some wacky spec like that which is IMO, nearly meaningless.

I would suggest that some scheme like this....linked, is a good place to start in any chat about amplifier REAL power into REAL loads.

http://www.audiograph.se/Downloads/PowerCube_12p_brochure_complete.pdf

'As to 150 watts and 45 amps? That's about 3.3 volts. Clearly something doesn't add up.
My panels are fused at 4 amps for mid/tweet. Figure 8 amps full tilt for the whole enchilada. Why would I need 45 amps?'

Well what does it all mean? Some very reputable companies always list this spec. Parasound and Harman Kardon come to mind. The bigger HK list 100 amps and the parasounds 60 amps. I have read some gurus that say amps are not even important. So I guess it's an audiophile thingy, i.e No answer. BTW, the link and the cube graphs etc.... are very similar to the method used to test amps in the Audio Critic. Better be careful. :)

Personally, I guess I'd fall on the 'amps is red herring' side of the fence.
Pass is the only amp manufacturer who lists VOLTS and watts. I also suspect his amps are nearly stable enough to either weld or charge batteries.
Audio Critic? I'll go have a look.
One thing to consider is Safe Operating Range of any semiconductor device. A power transistor, even with bigtime heat sinking can only take so much.
This is a wiki about SOR and explains it better than I can. To raise the stakes, multipe devices are paralleled.
http://en.wikipedia.org/wiki/Safe_operating_area

As near as I can figger', discussions like these really end up being about power supply.....mentioned or not.