Digital Room Correction: Where in the chain?

 Between your preamp and amp, I believe that’s what’s recommended by the MEN owner’s manual for your type of set up. Anywhere else will bypass some of the inputs and negate the whole endeavor for those bypassed inputs. From my listening demo of the unit the benefits far outweigh the down side of the ADC-DAC.

Yes, that’s the ‘only’ way the MEN220 works. And I it does seem most users are quite happy with the results. To rephrase my question - ideally, wouldn’t it be best to do any of that DSP upstream and eliminate the ADA? Is there a good alternative to the MEN220 approach?

The way the Legacy Audio Wavelet does it is after the outboard DAC or preamp. Then the final signal is sent to the amp. (And speakers if using the XD versions)

At that price I wouldn’t buy it without an in-home demo.  My experience is really good room correction can be more than worth the additional A-D-A conversion, but it can obviously vary depending on system, room, level of treatment, etc.  The other option is to buy used and hopefully sell at minimal loss if it doesn’t work out.  Best of luck. 

https://www.usaudiomart.com/details/650241532-mcintosh-men220-room-correction-system-complete/

The problem here is applying the correction to lp. It would be better to apply the correction to a digital signal, before the dac.  I assume most audiophiles resist disturbing the all-analogue chain of lp’s and tape (otherwise, what’s the point?) But if you want to apply digital signal correction to lp’s, you’re stuck with a conversion.  Putting the correction between the pre and amp at least avoids a double conversion for lp’s, but it will apply the double conversion to the digital signal. 
  Can’ you use the MEN (or something else, like Accuphase) as the sole dac? Does it have digital inputs and a volume control?  
 It challenges my deep audiophile prejudices to have 2 dacs in the chain, but it’s a trade-off.

+1 @lloydc that’s exactly my concern. And the MEN220 does not allow digital inputs. The digital is 24/192 in the MEN220, which on the surface sounds reassuring. But still…

Thank you @fthompson251 for pointing out the Legacy Audio Wavelet II. That system includes digital inputs and full preamp functionality. It also obviates my C53 and my existing DAC. This system gets rave reviews as well. 

Yes looks like that particular device is analog in and out only, so that’s how it works. You will have to try it and assess the results.  

Room correction is a must tweak for most any case where one expects best results with given acoustics, so doing it is a no brainer IMHO.   I’m confident the Mac device will do it well including A/D and D/A conversions needed. 

If you have analog  sources (phono, tape) this is pretty much the only way to roll!

I think you are on a good path, just do it right.  Good luck!

FWIW I have both analog and digital sources but do almost all my playback via streamer.  I convert analog vinyl and tape to digital using Audacity freeware (play once, stream many) and have no issues with the results compared to original analog source. The digital conversion captures all the nuances of the analog source perfectly.    Then I use Roon DSP for 1) room correction + 2) tweak the sound to my personal preference in each of several rooms in my house.   So been there done it and the results are beyond anything practically achievable in lieu of DSP.  I get every room tuned in perfectly to my ears which is a wonderful thing. 

The less expensive and easier alternative would be to ditch the Lumin and get a streamer that has EQ and/or room correction.

Don't hate on me, but I tried very expensive streamers and settled on the Eversolo DMP-A8 and A6 Master Edition for two of my systems.  IMO, used as streamers only, bypassing the DACs, they sound every bit as good as the more expensive ones I tried, maybe better in some ways and their app is far better.  I would have gone with a Lumin except for their dogma of not going down the path of EQ.  While I'm not a fan of DSP for room correct because I think it can make the sound 'thin', I do like the ability to adjust manually with a good EQ.

I personally think this is a better route as it requires less hardware, fewer wires and connections.... FWIW!