Prism makes the best AD & DA converters.
Reaper is one of (not the only, but one of) the top sound quality mix engines (ie 64bit fp).
Simple as that.
Those of us who can't afford Prism usually turn to Apogee.
Mac Pro 8x3.33GHz i7, 16GB, 120GB SSD(OS, apps), 3x2TB 7200 HD(data); MacBook Pro 2.8GHz, 6GB, 128GB SSD HD(OS, apps), 750GB 7200 HD(data); 2xTrue Precision 8; Apogee AD-16; 2xMOTU 828mk3, Evolution UC-33e; Faderport; WiRanger, iPad & the analog mixer has retired