Do I still need a DAC for a Logitech Transporter??

The AKM DAC in the TP is excellent, to my ears. I don't think you'd need an external unless you prefer a different set of qualities, or something in another league which would be very expensive. In that case you may as well get the DAC you want, skip the Transporter and just get a DUET or SB3 and feed the digital feed form that into your DAC of choice.

Do you think if I skip the Transporter and just get a DUET or SB3 and feed the digital feed to a DAC (PS audio Dac) that it will sound better than the Log Transport?

That would depend on the DAC (of course). As I said, it would take a pretty expensive DAC to significantly better the one in the TP, but there are various shades of personal preferences of how a DAC can sound. I use a Modwright Transporter so I really can't speculate on what a stock TP compares to. The TP is a very nice piece, but yes, you can accomplish the same thing with a good DAC and a wireless musical streaming device set up well. The TP is simply those things combined in one box. If you are looking for DACs that can compete at that price (street price of a stock TP is currently around $1250-1350 here on A'gon), I'd consider an MHDT Havana. I'd bet the Havana would give the stock TP DAC a run for its money.

Macdadtexas - Dan does not change the DAC in the Transporter for his Platinum Truth mod, it remains the stock AKM DAC - He changes the output stage to a tube-buffered output stage with tube rectification, and changes the power supply radically as well. The current MWTP is outstanding. Tube choices make a profound difference in how it sounds. There's a very long thread on tube rolling in the MW Audiocircle forum. (disclaimer: Dan is a client).