BAT vk-3ix and Parasound Halo A21 match?

I've used my 3ix with a Bryston 3B-SST, which has an input impedance of 10k/leg balanced. It is a few dB down at 20 Hz (measured with a voltmeter at the amp outputs), but nothing disastrous. The Parasound should be fine.

Here's what BAT has to say on this issue:

"Is the requirement for minimum input resistance dictated by the output resistance of your preamps?

No. However, this is a popular misconception. It is common to apply some old rules-of -thumb to things like preamplifier to power amplifier interfaces and state that there should be some magic ratio between the output resistance of the preamp and the input resistance of its load. People commonly mention numbers in the 10:1 or 20:1 area, some as high as 100:1. Unfortunately, there is no truth to such claims. As many of us know, one can perfectly transmit a signal in a system where the load impedance is equal or even lower than the source impedance (witness any cable TV system). The unusual design of Balanced Audio Technology's preamplifiers allows their gain stages to drive loads with resistance much below what their specified output resistance ratings would imply. For example, the VK-50SE preamplifier can supply a load with 65mA peak current - an amount well beyond that of the great majority of preamplifiers on the market today. However, it is also important to understand the role of the output coupling capacitor, present at the output of BAT preamplifiers. It is the size of this capacitor that will dictate the minimum power amplifier input impedance, not the output resistance of the preamp."

Having owned a 3ix for several years, I've been down this road (even owned a BAT 250SE SS amp for a while.)

If you like the 3ix, I would not limit the amp search to those with 100k Ohm or above input impedance.

Atkinson measures the frequency response with a 600 Ohm load and 100k Ohm load, which is very unhelpful as no consumer amps are anywhere near a 600 Ohm load and most are below 100k Ohm. A 10k Ohm load would have shown the response to be down a few dB at the frequency extremes.

BAT's stated spec of 10k Ohm is a sensible minimum bound for the amp's input impedence. 66k Ohm is no problem for it at all.

Yeah, sometimes the balanced impedance is given as the sum of the legs, and sometimes as per leg, which is a source of confusion.

A few dB down at 20 Hz is not something I'd *aim* for, but it doesn't really effect the audible result. The Bryston still has that solid bass foundation that these amps are known for even when fed by the 3iX.

I'm currently using my 3iX with the Rogue M-180 monoblocks, with excellent results. These have a balanced input impedance that sums to about 75k Ohm (the specs on the Rogue website are either for an earlier iteration or wrong. See JA's measurements of the M-180s.)