Do I need a 20 amp or 15 amp power conditioner/surge protector

I have a Dan D'Agostino Progression Stereo amp that has a 3,000 VA power supply transformer coupled to 400,000 microfarads of power supply storage capacitance.  It's a true triple down amp rated at 300 Watts into 8 Ohms, 600 Watts into 4 Ohms, and 1200 watts into 2 Ohms. I'm using a pair of Magnepan 3.7i's which are rated at 4 Ohms. 

One of the odd things is that the amp comes with 20 amp power cord that has a 20-amp IEC connector at the amplifier end and a three-conductor 15 amp AC plug at the other end. The instruction manual tells you to plug it into a 15 amp wall receptacle. 

After a recent scare, I decided I should get some protection as well as clean up the AC being fed to my components. My LAD explained to me that the minimum I should get is the Niagara 5000 because it's rate for 20 amps, but when I asked why does my amp need that when it's plugged into a 15 amp receptacle, he said that at high loads, the amp may be pulling a little more than 15 amps and power conditioner rated at 15 amps would restrict that and the audio quality would suffer. 

So, here I am trying to figure this out, I mean, my LAD may have point since the amp manufacturer supplies a 20 amp cord, but tells you to plug it into a 15 amp receptacle, but I just don't know. For the price point I'm looking at, I've narrowed it down to either the Furman ELITE20 (20 amp) or AudioQuest Niagara 1200 (15 amp). Do I really need a power conditioner rated at 20 amps, or will one rated at 15 amps be fine? Also, is it really possible under heavy load my amp could actually pull more than 15 amps out of a 15 amp receptacle? Very confusing... Thanks for any clarity you can provide. -cheers!