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

Not at present time Eric.
However I do not like not having the option to try an Atmos setup if I decide I wanted to.

And again, there are no future software upgrades for the avp18 ever so it is basically now obsolete if you will.

The AVM 60 does not have amps in it. I have the lower 720 Anthem (with amps) and I would absolutely go with the 60. You also get great room correction.

I've never turned on the amps in the 720 since day one. I immediately hooked up an external amp to my 5.1 system.

Good luck

First thing.  Dolby Atmos and DTS:X surround formats are fully backward compatible.  That means that you can play an Atmos movie on a system that does not support Atmos and the movie/sound will play just fine.

Second, the newer 4K processors are only good if you have a 4K source.  Some of the streaming sources will have 4K.  So it's up to you as to whether or not you really want to support 4K.  Some of the newer processors may have some additional video processing chips that could help.  I'm not sure how much. 

If you want both 4K and Atmos support, probably the best processor for the money is Marantz AV7703 (or higher).  Marantz is an excellent processor with discrete analog stages and great power supply, but it is voiced just slightly on the warm side with rolled off high frequencies.  You should be able to get one for under $2k no problem.  They are on ebay all the time (AV7703 / AV7704 / AV7705).  They support the latest HDMI 2.0 and HDCP 2.2 standards.

The AVM 60 is going to have much more high frequency response and could sound a lot more exciting, but it could come across a little bright and I don't think it will have as much fullness and body as the Marantz.

If you want to remove your 4K or atmos requirements, there are a lot of options.  Such as Classe SSP800 or an Anthem D2v if you can find one.  Heck, even the $1k Outlaw Audio 976 processor is not bad (I've tested it).

The Nuforce AVP-18 is really a bare bones processor (switching power supply and SMD op amps for output).  There's hardly anything inside and you have a LOT of options for a significantly better processor.

Thanks Auxinput.

Yep the avp18 is a basic boogie box for sure but it has been/ is reliable and has done its job.
Will be looking up the Marantz models although they seem huge and bulky and I do like the slimline look of the avp18 I must admit.
We do have 4k tv and 4k streaming service and not into the Atmos right now but always nice to have options.

For reference, there's an internal pic of your AVP here.  It actually looks very similar to the low-end processors that Emotiva has offered over the last several years:

https://www.audiosciencereview.com/forum/index.php?threads/the-rise-of-audio-negociants.14384/

Generally speaking, slimline and audio quality don't really go together, especially on processors.  There's a reason for that.  It takes space for a good transformer linear power supply as well as all the DAC and audio outboard board circuits.  I cannot find a good pic of the 7703/7704/7705, but the Marantz is packed full of layers of circuit boards.  The Anthem AVM50 is not quite as big, but it's still larger and full of boards.

Probably the best "slimline" type of processor I know is the Krell Foundation 4K, which is excellent, but now you're looking at $4.5k used.  It's only 3.5" high!