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
@lowrider57 so do u think replacing the bad tube would fix the bass response problem? Could this be the culprit of the low bass sound overall? 
Preamp tubes are replaced in pairs. Two in the front, two in back. If the pair that supplies gain to the preamp are bad or weak, then there's not enough juice to drive the amp.

Look at the manual and identify which tube is bad...
V1 V2 V3 V4

You could, but the other tube could go bad at any time since you don't know it's age. When you replace the pair they will both be strong tubes.