You could use your SACD player as a transport into a brad new DAC with all the flexibility you are looking for. and still go direct from your SACD player into your preamp.
remember - you generally cannot get sacd into a digital stream...because it is encoded. thus you usually need to play sacd within a dedicated sacd player. you cannot play sacd thru the digital out unless it is into an encrypted output that goes into a dac by the same manufacturer.
If you get a separate DAC with the flexibility you seek, then when you play USB, you go usb to dac to preamp. When you play sacd, you go sacd player to preamp. and you can experiment by going CD thru your marantz direct to preamp...or thru the dac to see if the dac is better.
remember - you generally cannot get sacd into a digital stream...because it is encoded. thus you usually need to play sacd within a dedicated sacd player. you cannot play sacd thru the digital out unless it is into an encrypted output that goes into a dac by the same manufacturer.
If you get a separate DAC with the flexibility you seek, then when you play USB, you go usb to dac to preamp. When you play sacd, you go sacd player to preamp. and you can experiment by going CD thru your marantz direct to preamp...or thru the dac to see if the dac is better.