Roscoe, et. al.,
I think th Tascam is going to become a project. I found some information concerning a modification to the input stage made by Dave Garrelson on Audio Asylum.
https://www.audioasylum.com/audio/vinyl/messages/116/1163057.htmlHe is using Panasonic FM capacitors, and bypassing them with film capacitors. These 8 capacitors (47uF/35V) are coupling capacitors in the ADC input. Frankly, I am not sure if they are actually required, but there may be some issues with DC on the input or output of the differential amplifier stage. So my inclination is to use ELNA Silmic II (RFS) capacitors that actually sound great without a bypass. They are a little larger (10mm dia), but if I stagger the caps, they should fit fine. The other change is to increase the DC voltage capacitors for each opamp, from 22uF to 100uF. Althogh theses are 50V rated, the circuit does not see anything this high, so a 35V capacitor should do fine. Will probably use ELNA Silmics here as well, though very low ESR caps would help out. Actually, the caps I am removing from the signal path would do fine if save to recycle, they are a higher performance cap than installed already.
I have to think about the opamps used in the circuit. I can get SMD (SOIC to DIP) adapters, and using flux and ChipQuik, remove the opamps on the board and replace with the adapters. But that may be later.
David