Do I need a dac

If external DACs quality and specs will be at least like your T2 internal DAC or better, SQ will improve.

Hello, 

The T2 is really great and great for the money as long as you use the internal DAC. 
The only thing I would suggest is a linear power supply. If you are out of warranty you can use a $400 SBooster. If in warranty you would void the warranty if using a LPS from a third party like SBooster. It makes a big difference. If you are willing to try a different preamp then Lumin just released the P1. It is an all in one preamp, DAC, and streamer with a LPS already built in. Plus, they say the sound beats ghe T2 and almost as good as the Lumin X1. I am in line to do an at hone demo. This store in the Chicagoland area is a Lumin/ SBOOSTER dealer. You can even demo the LPS for the T2 in your home. 
holmaudio.com

I think you would be good either way. I hope this helped. 

If I had your preamp, which I think is awesome, I’d get a better DAC.  Not that the DAC in the Lumin is bad at all and I’m sure it’s not, but I think you can do better depending on your tastes. 

I bought a aesthetix pandors eclipse dac and wow what a difference