You must use a DAC that works with your Sony Changer. If I remember correctly the Sony's come with a Toslink output and perhaps a SPDIF. So you cannot use USB.
You can find DACs that accept both USB and Toslink/SPDIF. Some will switch automatically depending on where the signal is coming from.
Probably the most cost effective thing to do is to rip all of the CDs in Sony to hard drive and just use the SB3 for everything. Even if you have to buy new hard drives, it will be less then half of what you are planning to spend on another DAC - and you already know that you like the sound of the SB3 - no guarantees with the Sony/DAC combo.
You can find DACs that accept both USB and Toslink/SPDIF. Some will switch automatically depending on where the signal is coming from.
Probably the most cost effective thing to do is to rip all of the CDs in Sony to hard drive and just use the SB3 for everything. Even if you have to buy new hard drives, it will be less then half of what you are planning to spend on another DAC - and you already know that you like the sound of the SB3 - no guarantees with the Sony/DAC combo.