I tried a 4 stereo stems mixdown on a Soundcraft compact10 with a RME Fireface 800. With no eqs just summing the results were initially impressive yet on blind testing the Digital sum inside the box always wins out with clarity and detail.

where there any audible benefits with the analogue summing in your opinion, even if it was not clarity and detail...

Analog summing makes a big difference. More headroom=punchier sound...Unless your running your whole thing through an L2. The Empirical Labs Fatso is kinda like a stripped down distressor and makes almost anything sound better. I almost always run my synths into a DI into a pre. It just fills things right up. I'd take a good DI and stereo preamp over compression, etc any day. Software w UAD, Waves, Sonnox is great for EQ and comp, but you can't emulate a nice transformer.

Oh, the summing thing is about the last thing you want to worry about. Front end first, start with a source worth recording then get good pre amps and conversion first....

Most important outboard gear is monitors. If you can't hear what you're doing there's no point and you won't appreciate the subtleties anyway. Ideally, you've got SPACE to listen to them in. No, headphones are not the same, but if you're in a flat or whatever then get some proper headphones, a few pair even.