Full Mod it !!!
and get a moded elpac power supply.
It will cost about twice than the SB3 itself, buy it will take it to a whole different level, J/K.
I suggest you will start to listen to it as it is, cuse it really is a great source even in stock.
When you get the next "Upgradities", start finding out on SB3 upgrades.
What is your dac again ?
Unless you have a nice dac, I suggest you use the analog output for both connections, it is very good.
I guess you will need to have some sort of Y splitter for the Analog output.
Try to use Losseless audio as much as you can, try to use the volume level on the SB3 as high as you can(and use your amp volume attenuation), it has digital volume attenutation, It has been improved in the latest version, but I still think it can degrade sound, maybe with a high level of attenuation(getting the volume bar under a certain threshold).
When using the Digital output, You can set the volume to be
fixed or
variable, fixed means full signal level which bypases the volume attenuation (it wont be affected when you change the volume on the SB3).
Variable output means the signal level at the output will be varied by the volume settings on the SB3.
If you are going to connect it to a speaker setup, you can use the SB3 straight into a power amp, as the SB3 can act as a pre amp (volume attenuation).
So if you do have one, you can try using it straight out of the SB3, if from the digital, than it will be: Computer->SB3(digital)->DAC->Power Amp-> Speaker.
With analog:
Computer->SB3(analog)->Power Amp-> Speaker.
I assume you wanted to connect the digital output to your Headfive(DAC), but IMO the SB3 analog output will be better, you are more than welcome to try and see for yourself.
I heared some people did it and reported working pretty well.
I am talking way too much and I better stop now
Good luck