Suggestions for replacement for my old Nuforce AVP-18 surround sound processor

You get what you pay for most times.

I did see that on the Krell for HDMI, the one I am watching supports 4k.

However at this price the Anthem avm60 is still a very worthy contender and in black it did not get a thumbs down from the better half so still have options.

I have been looking at this Classe item as well but know nothing about it, anybody?

https://www.audiogon.com/listings/lisa3aed-classe-audio-sigma-ssp-surround-sound-processor-processors

I keep forgetting about that processor, mostly because it only has balanced XLR outputs for left/right, but since you are only going to use RCA interconnects to your amp, it shouldn't matter to you.  The Sigma SSP uses the same audio stages as the previous SSP-800 (which is a fully balanced design).  The Sigma is only 3-3/4" high, which is excellent for you.  However, the Sigma SSP also had two versions just like Krell Foundation.  The original only supports HDMI 1.4 and 1080p.  The newer "mkii" version will support HDMI 2.0 and 4K UHD and some limited Atmos decoding.  Here's a "mkii" version for a little more at $2799:

https://www.audiogon.com/listings/lisa4f8g-classe-sigma-ssp-mkii-7-1-channel-home-theater-processor-...

That being said, the Sigma SSP uses switching power supply for everything.  Since your AVP-18 also uses switching power supply, it's probably not a big deal for you.  The Sigma SSP will still be a significant upgrade from your AVP-18 in all areas.

I think the Krell Foundation will still have better sound quality.  One of the things I really like about the Krell design approach is that they use linear power supplies for everything, including both digital control circuits and DAC VREF power supply.  Most processors will use a linear power supply for analog sections, but still use switching power supply for digital sections.  I think the Foundation is going to sound smoother, fully and more natural than the Sigma SSP, but it's going to be $1700 more, lol.  The Sigma SSP will still be a huge improvement over your AVP-18, though.  I guess it depends how much you really want to spend, lol.

Yes, two flavor of SSP and I see the TMR one started as a mk1 and was updated to mk2($1000).
Better value to buy the already updated one obviously!

Her who must be obeyed prefers the look of the SSP and as it is not an ultimate endgame HT rig I think it would be just fine.
As you say a big improvement on the avp18 for sure.
And many thanks Auxinput for all your help and advice on this thread, sure been a huge help!

yeah, unfortunately, me and many others think that Krell failed big time on the asthetics of their current line.  The previous Evolution line looked a LOT better, much like a Mercedes.  The current line looks cheap, like a Toyota, but the build quality is still excellent.