Yeah...with the combination "interfaces"...there's more to the picture than just the converter section, so you have to consider all those other things when talking upgrade...
...but AFA just the converters...while there have been new ones put out every year, and many with all the very high rates...I think you need to upgrade a lot more in the studio environment before going to them.
Now there may be some validity to having a higher end of stereo converters for monitoring specifically...but I never understood why people only think you need those higher Q converters for the monitoring. IMO...you would/should have the same Q on the A/D as you do on the D/A....and I actually think the A/D would be more important, because once your audio is converted, that's it...that IS what your are monitoring.
That said...I kinda get why many opt for a high-end stereo D/A converter, so that as they mix that tracks, they can hear the extended audio quality of the mix...which may no be as critical as some of the the individual track audio quality.
I don't use combi "interfaces"...but I have been using the same converters for the last 15+ years now.
I've got 24 channels of A/D and D/A from 3 Layla24 boxes. I've got them clocked with a Lucid SSG box...works great.
Actually... have the ability to go to 32 channels, as I have one of the very, very rare Layla "extension" boxes, that allows you to piggyback off one of the others, without the need to a 4th PCI card...you just use the on-board ADAT connections between them, and you have an additional 8 channels of A/D and D/A.
Just haven't had the need to, since I'm working with a 24 channel tape deck...so "24" is a nice number...but I've been thinking about connecting it so I could have 32 channels on mixdown coming out of my DAW to the console...instead of the 24 I've been use to.
I actually have a rack slot waiting for that 4th Layla box...just been lazy.