@dmac67 Consider the resale value of modified gear can often be compromised.
As for the compatibility of your Krell 400xi integrated with Thiel 3.6’s:
Thiel CS3.6 loudspeaker Specifications | Stereophile.com Thiel CS3.6 loudspeaker Measurements | Stereophile.com Krell KAV-400xi integrated amplifier Specifications | Stereophile.com Krell KAV-400xi integrated amplifier Measurements | Stereophile.com We can see from the above links that the Thiel CS 3.6’s impedance stays well below 4 Ohms most of the time. We can also see from the above links, that unlike some, but not all (!) of the rightfully famous, for their ability to keep on doubling down power into lower impedances, Krell separate power amplifiers, that the Krell 400xi integrated is not rated for sub 4 Ohm loads, nor could it withstand the rigors of measurement testing into such loads. If your interested in Thiel CS 3.6’s, you would do well to consider different amplification. There are only a few, usually expensive, integrateds that are up to the task; some of the Gryphons and the DanDagastino Momentum amongst them.