The best sound I have heard is the analog outputs of a modded SB direct into a power amp with no preamp, DAC or anything else in the way of the signal.
If you put anything else in the signal path, it WILL change the sound.
Now what sounds best and what is practical can be two different things. If you want to run two sources into an amp, then you need at least a switch. If you want to use a TT, then you will need the preamp for the phono, volume control and then a switch. The signal path gets longer and more circuitry gets involved.
My thoughts would be to get the Full mod done to your SB and then compare the sound of the modded analog SB to the sound of the digital out through the DAC 1. If your prefer the sound of the analog out of the SB, you can sell the DAC 1 and come out ahead.