how much power

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.

Magfan, Rok2id,
45 amps is peak current that has nothing to do with operating continuous collector voltage of amplifier.
Continuous current would probably be in the range of 1...2 amps.
What is necessary for amplifier to deliver the same power onto the 4Ohm load vs. 8Ohms is to double the current and not on peak or transient bases but on continous.
Not all amps are capable to weld but there are some.

'What is necessary for amplifier to deliver the same power onto the 4Ohm load vs. 8Ohms is to double the current and not on peak or transient bases but on continous.'

Then, would it be accurate to say that a true 'high current' amp will double the current (continous) when the load is halved?
What, if anything, does this say about the quality of an amp? I am trying to decide between the Harman Kardon HK 990 and the Parasound New Classic 2250. The HK doubles, the Parasound does not, but it's watts per channel is greater into 4 & 8 than the HK. The parasound list 45 amps and the HK 100amps. From just this information, can any conclusions be drawn as to which is the better quality amp?
BTW, thanks for your answer.

whichever you prefer. I wouldn't let an amps amps decide anything for me.

Someone needs to tell me how an amp can peak 45 amps and NOT drag the powersupply down to a low voltage, regulation or not. Even if you dump a huge capacitor bank, you than must contend with 200 watt transistors above designed limits.

power is watts, = volts x amps

Unless we are going back to the days of IPP (instant peak power) a scheme whereby an amp with a door bell size transformer can be said to have 500 watts.

As for doubling up? This is 'the law' for panel speaker users, like myself. howver, I'd rather have an amp with 400 watts at 4 or 8 ohms than an amp which doubles up from 100watts @8.

I think NAD may be on to something with continuous ratings being the same across impedance, but an ever increasing dynamic power as impedance drops. No mention ever of 'amps'.

Rok2id,

Are you familiar with the unique design of the HK 990?

The unit's preamp section offers the kind of DSP that you would usually find only in a multi-channel AVR or pre-pro. (It has ADC, DAC, digital bass management, digital room EQ, etc.) Personally, I think it's an incredibly good idea, but it's definitely not the usual "audiophile approved" approach. I'd love to endorse it, but unfortunately, it's well nigh impossible to find one to audition and I've never heard one. However, if you listen primarily to digital sources, this thing has unique capabilities among 2 channel amps.

My point is that, the HK 990's power amp section, while a highly regarded design (see below) isn't really what PRIMARILY distinguishes this unit from the Parasound (or anything else, really).

That power amp section itself follows the Matti Otala Citation design principles established decades ago. Many people (me included) like the sound of these amps very much. A lot has been written about this clever design and a quick Google search (try "citation amp" or "Matti Otala amp design") will probably be educational for you. In the end, however, the overall "sound" of the HK990 will be much more influenced by the DSP in the preamp section - if you use it.

Good Luck.

Marty