Is a preamp needed ???

It depends. I would encourage you to scan these pages, as there are many threads about this subject already......

I would imagine a quick call to a Lumin dealer would get you an answer.

What amps you’re using....tube or SS. Depending on rest of your system, you may be alright with Lumin T2.  

What other digital sources you’re referring to? T2 will only allow you hear music stored on a external HDD. It does not have any analog inputs you typically found on a preamp. 

In any case, I would bring in the T2 in your system and let your ears guide you.