I've just purchased a MX121. It's fabulous for movies and is a big upgrade over my previous Marantz 8003. For music though, the D100 DAC + C2300 preamp is superior. I'm hoping to try the D100 with the MX121 this weekend and see how that compares to the D100 + C2300 combo.
If you're not bothered about the latest and greatest (Atmos, etc) or your wife won't allow more than 5 speakers in the room where you have the MX121 I say go for it! Also looks great next to the rest of the Mac gear.
Rm1: Turntable: VPI ScoutMaster Signature Cart: Dynavector 20*2L Phono: Audia Flight DAC: Lampizator Atlantic Preamp: Mac C500T Amp: Mac MC7270 Headphone amp: Glenn 300B Headphones: LCD-3F
Rm2: DAC: Mac D100 Prepro: Mac MX121 Amps: Mac MC7270, MC7108 Speakers: B&W 804S, Totems