chinese tube pre amp

Hello, I recently bought an ART DJPRE II to replace my modded Fosi Audio X2 because it distorted at higher levels than the normal 39 dB. The problem is I can't really tell which one is really better, it seems to me that the Fosi is kinda brighter or as more resolution and the DJPRE II is darker...

Need expert's opinion about Chinese Tube buffer or Pre-amp Like FX audio tube 01, YAQIN SD-CD3 etc.. Which can be used with integrated amplifier or Power amplifier... I am using Audiolab 6000a integrated amp with Tannoy revolution xt6f speaker. Will there be any improvement of sound? Want some...