It is an interesting point. I believe the reason your mixes right now may not sound as good as the best released material is more to do with your engineering and less to do with outboard gear and summing being used externally.
Once a time perhaps the finest analog gear reigned supreme but because it was invented and built we are able to model it so well digitally now. You definitely can create a huge fat sounding analog mix with all the qualities you desire and all ITB as well. You have got to just keep persisting and getting better and better at doing that.
I have come right over from the very analog world to ITB operations now and I must say not only has the sound remained great it has improved as well. Better transients, lots of things. Noise has gone now. And yes digital may have been a bit cold sounding at day one but it has really evolved from there to what we have now. And that is the ability to take on any persona we want it to be which is even better. It can be transparent but also it can sound like something else. That is cool and clever. Analog gear cannot do that, it is stuck on one sound.
I was a full analog/digital hardware synth guy too but now I don't have any and the plugins are sounding so great it is just incredible. And what about new synths that have never been heard before like Alchemy, Prism or IRIS. Their sound quality is breathtaking and it's getting better every day. If you think plugins cannot match the finest hardware you are just wrong.
I am reading more and more everyday about the blind A/B tests they do in reviews with plugins vs hardware and mix consoles being modeled and all and a lot of the time even great ears are not picking the difference. I have just bought a Pultec EQ for a no brainer for $30 and I am amazed at how great it sounds. It sounds bloody fantastic actually. This plug transforms how a track sounds immediately! I have used the real Pultec before, not a lot but I remember how nice it made things sound. This plugin is so much like it. I use to own Roland Dimension D chorus. I loved it but sold it. There are ones going around here for $800! How stupid. Who would pay $800 for a Dimension D. I got the plugin from EmptyRoomSystmes, a company that was mentioned in these very forums and thanks very much to that person! It sounds killer and exactly like I mean exactly the same as the original.
(superior to UAD,apparently!) The Plugin is bit better. The crappy analog noise has gone and it sounds a little nicer than the original on some things with transients.
(you can always put the noise back in if you really want it! and you can EQ it to sound identical to the original as well) So now it's down to crafty engineering practices again. Let's use some channel strips here and there, Dimension on one of the clean guitars, the Pultec over some busses for a final EQ. Some great compressors here and there as well to add glue. Things are starting to sound better. I think you have got to be prepared to actually engineer stuff and stop leaving too much alone with no plugins or anything being done to the tracks. There is always something you can do to make a track sound better even if it's just a little better or a lot better. I am always also for great recording technique giving you a great sounding track to start with too and it's nice at times to use the hi fi approach of minimal degradation to the signal quality if possible.
I think digital can create the entire sound of a complete analog system and also add in parts of the mix in a transparent manner as well not going through anything analog. The digital technology can do it today so why get with the program and get in there and just learn to be a even greater engineer using a medium that is superior in so many ways and is offering the possibilities of sound manipulation on a level never seen before.