Eboz his experience is typical.
A stock SB with stock power supply plays like a cheap to medium level cd player, for instance there is not so much difference between that and my respected Philips DVD 963SA with XO3 clock and upamp upgrade, the Philips is a little more extended, and has a little wider soundstage with more room, but I wouldnt be surprised if many cant hear the difference.
The upgrade power supply, which comes in huge varieties, CAN improve the sound but it depends on your setup. This is because the socalled noise from the stock power supply CAN creep into your other equipment, like your amplifier, and contaminate the signal.
A test can be done with an AM radio if you have one, reception of AM programming can be very difficult with a switched power supply in the vicinity of the radio.
Those that have equipment that are immune to outside noise so to speak wil probably not hear any difference in the sound quality changing the power supply. This is what Max F said also.
Anyway, a separate dac is so much more an upgrade, the power supply upgrade is hard worth thinking about unless you are really picky, and curious, and well, most of us are.....arent we ?
A separate dac wil put the SB3 in the same class as a high end cd player, the 3 dimensionality appear, the music frees itself from the speakers etc etc.
So, frankly the stock SB3 is perfectly okay, but is you are used to audiophile sound it wont take you long to pair it with your favourite dac.
Quote from Stereophile when they tested the Bryston B100-DA SST :
After burning in the B100-DA SST by
having it drive my Quad ESL-989s, I
began feeding its DAC digital signals
from my Krell KRC-28 CD player and
the Slim Devices Squeezebox, which
let me compare CD and wireless
sources. Listening to “Too Rich for My
Blood,” from Patricia Barber’s Café
Blue (CD, Premonition/Blue Note 5
21810 2), I could detect no difference
between the digital outputs of the Krell
playing the CD and the Squeezebox
playing the losslessly compressed file of
the same track through the B100-DA’s
internal DAC—but both digital sources
were decidedly better than the SB’s
internal DAC feeding an analog signal
to the B100-DA. For the bulk of my
listening, I listened only to streaming
digital files fed to the B100-DA.
Through its own internal DAC, the
B100-DA’s bass response reminded me
strongly of the Bryston 3B-ST’s.