You have to take into account the echo effect applied by the SNES's DSP, which apparently they replicated manually on the DS like you mentioned there. I'd say the "most accurate" it's the original of course, but I guess you'd have to take inspiration from both sources if you want to get the best sound.
Also, few questions... Why the Namco expansion? How many channels are you going to use? Do you want to make a 1:1 version or a proper adaptation?