Audio Research VT100 MK1 and LS15 HELP!!!


I recently bought this set VT100MK1 and preamp LS15 and while I was at this seller house he demonstrated the sound from his online Tidal on TV connect optical to the DAC Luxman DA - 06 then this go to the preamp LS15 and out into the VT100. This set up sounds amazing at his house. However, when I came home play CD from the Sony X1100ES Blu-ray player RCA output into the LS15 and out to the VT100 and it sound horrible - no bass at all in any type of music.  The sound sometime muffle and not clear and most importantly the bass missing tremendously. Im using a pair of KEF R900 Speakers. What is wrong here? can anyone help me correct the sounds? it is because I didn’t have the Luxman DA - 06 DAC? or it is because I don’t have those fancy hundred - thousands of dollars cable?  or the CD source is playin at 41khz /16 bit not high enough signal?  

This is my first system and I don’t know why I can’t get that high fidelity sound from the ARC equipments.  I'm waiting for the Audioengine B1 to arrive so I can stream Spotify into the LS15.   What is wrong with my set up?  Thank you in advance for helping me solve this.
kentrent
@jea48 

the tubes was replaced 8 months ago with brand new tubes from arc. I do hear bass from the bass driver but overall sound quality the bass is missing that punch greatly compared when im using another amp like the old vintage 1965 MAC1500    

The difference between my set up and the seller is he he Tidal streaming into the DAC then goes into the preamp LS15.  Could it be the DAC that i didnt use and the source is Sony Blu-Ray player?
@lowrider57 he was using rca into the preamp not balance.  I asked him and he said the DAC will fix my problem. Im not sure if he’s right
The only difference is the dac most likely has a higher gain than your CDP.
That doesn't explain why you have poor bass response. 
@lowrider57 u are absolutely right about the Dac help gain.  At the seller house setup, he only turn on 30% and i can hear music pretty loud. But when my setup i had to crank up to about 70% to hear loud.  So definitely this confirmed that DAC increase gain.  But i cant explain why my arc setup is low bass response.  I’m kinda sad and disappointed that i spend a lot of money but im not getting the sound i want.  Idk what’s wrong...