Frequency Response Measurement Question

I am running frequency response measurements on my system using a RS Digital meter and Rives Audio Test Tone CD. I use both the 1/3 octave tones and the 1/6 octave for bass response.

My question is this: I just changed amplifiers and am finding very different response curves even though:
1. Speaker placement is identical.
2. Measurement position is identical.
3. Source and cabling is identical Including power cord. (I run a dedicated circuit and wall outlet for the amp and DAC. Everything else is on a separate circuit)
4. Power rating of amps is very similar.

Why is this given both amps are fairly high quality and should produce a fairly flat frequency response? Since the setup is nearly identical, it seems this is not the room response but rather a difference in the amplifiers.

The problem is, I have a fairly flat response but with a big bump at 2000 hz - which is a noticeably bad place to have a loud spot, in other ways high frequency is flatter with the new amp. Any ideas on how to address this.

Equipment:
Green Mountain Europa Speakers
Monarchy DAC 24 (Solid State section used for both)
Integra CD player for transport.
Paradigm PW-2100 sub, converted to down firing.
Cobalt Ultimate Speaker cables
Blue Jeans interconnects

1st amp - Arcam AVR 300 in direct mode, 2 channels used, 120 watts approx..
I actually really liked the sound of this amp but wanted to simplify since I no longer am building home theater.

New amp - Simaudio I-5, 110 watts at 4 ohms.
In this setup, this amp has more clarity and sounds more powerful (dynamic?) but less transparency with less separation between instruments and exhibits a harshness (the 2k bump I suspect). So if I could find a way to fix that, I think it would sound great.

Thanks in advance for your input!!!