Good luck researching! Imho the BillD C-1 is well worth the money, and is the best value for your money. To find equivalent sound quality in a pre amp , you would probably spend 2x or 3x as much!
Enjoy it my friend! I keep going back to mine after trying other gear!
I have a C-11 with a BillD mod by Dennis! I love it, I am currently using a Carver 900 reciever wile I make a few minor fixes on my C-11. I had distortion in my headphone amp! I will put my c-11 back in service when I get my top cover back from Kevin next week! He took it to Carverfest for the Bobfather to sign!
As always enjoy the music!
BarryG