Krell Trio 300 vs. Krell Trio 300 XD

But does the XD upgrade specifically address nd_72’s issues?

I"m not sure. I don't know what amp solid state amp would be considered less bright than the new Krell amps XD or non-XD. I'm a long time Mcintosh amplifier owner. I'd say the Duo 300 XD is not any brighter than the new Mcintosh MC611. Never thought I'd be saying that in a comparison of Krell and Mcintosh. If I had to pick, I'd say the Duo 300 is less bright then the MC611. The "house sound" of both companies seems to have moved in opposite directions from their old sound.

Thank you all for comments. I sent my TRIO 300 for an XD upgrade directly to Krell. It turns out they upgrade older models to XD for $1,450.00 + shipping costs. The customer service at Krell was amazing. I got a call from the Krell’s CEO with an update and he spent good 10 minutes with me on the phone explaining advantages of XD. He also gave me his cell phone number if I need anything in the future or have questions. Truly remarkable. Amp came back looking brand new. They also included XD badge on the front panel.

Now, when it comes to the sound. To be honest, I am struggling to pick up on the difference. Maybe if you could switch XD on and off if would become more apparent, but in my opinion this amp sounds great with or without XD upgrade. Perhaps I should upgrade my speakers to take full advantage of this amp, my 10+ year old ML ESLs may be looking for new home soon.

Can anyone recommend speakers for this amp? The two I am thinking of are ML 15A, or KEF Blade 2s

I was able to compare both XD and non-XD in same system. The tonal  characteristics don't change. A lot more information passes through the XD than the non-XD. Imaging is a lot more 3D in XD and that's where the greatest improvement is for me.  I missed my Mcintosh monoblock's imaging before hearing the XD model. Now I have what I always wanted my Mcintosh to be,  extremely dynamic, tube-amp like imaging , and non-fatiguing. 

I have Mcintosh XR200 speakers and while I love the speakers, I always felt I would like a more dynamic speaker. I've tried a few brands but none were able to change the fundamental dynamics of the speakers until Krell both XD and non-XD. The Krell amps were already dynamic and I don't hear much difference there between XD and non XD.

The only set-ups that match the Krell XD stuff is bi-amping with a tube amp on the mids and highs and a dynamic solid state amp on the bottom end. The Krell XD stuff can just do it all in one box.

I have the 375 XD monos.  Had a 300 Duo.  I absolutely love the XD amps. They do it all...soundstage...imaging..great highs and lows...best controlled bass ever...I can listen for hours.