Pre-amp necesssary ?

[Deaf Cat]

Hiya,

If one only has a:
SB2,
or SB2 & DAC,
or modified SB2,
or Transporter,
as an analogue source,

Would it be a plus for audio quality to employ the use of a pre-amp, or just use the volume control on the SB/Porter ?

I'm understanding passive and active pre-amp stages make a difference, as to whats what I'm unsure?

Thanks for any thoughts