Because I have a lot of headphone amplifiers and want to play all of them at the same time simultaneously. (Like Zeos does:)) Using USB you can only select one device. The rest amplifiers are working via Toslink splitter or XLR and RCA cables. Topping 7pro and D90 don't have digital coax output. Only 7s has. As a source I use Cambridge Audio D850 and Topping 7S, as my Toslink splitter can receive Coax and Toslink signal (switchable) and split this signal into 8 toslink outputs. Thats why my choice is 7S.
List of my setup equipments: 2x Oppo Ha-1 (Black and Silver), Burson Audio V2, Pioneer U-5, Pathos Aurium, La Figaro 339, Schiit Joutenhem, Topping 7s, Topping A90, Denon PMA-50, Oppo Ha-2, THX AAA-789x 2units, Cavali Tube Hybrid (CTH), R2R artist, Sennheiser GSX 1000, SMSL SU-8, 2x Standard Balanced DACs, Emotiva BassX 100 and more, more small items. Pictures of my setup somewhere under my profile discussions.