Digital Audio and Yaqin SD-CD3 Tube Buffer?

I'm running a computer-based desktop audio system playing through Audioengine A2+ powered speakers and I was considering placing a Yaqin SD-CD3 Tube buffer between the PC's sound card and the powered speakers.  Before I moved forward, I wanted to know if others have tried using a tube buffer in a digital audio set-up and what their results were (even if not this specific model).  I am worried that whatever tube characteristics the Yaqin might add will be lost in the processing by the powered speakers.  Is this likely?

More specifically, I wondered if anyone had suggestions for tube replacements for the SD-CD3 (6SN7's) as I understand much better results can be gained by replacing the stock tubes.
I tried CD2 version (I think) of Yaqin - and do not remember being overly impressed, it just muffled the sound.
I think your better bet (and for similar price) will be external USB dac with tube output - (such as Maverick Audio or similar). It will provide superior D->A conversion as well when compared with PC.
Thanks for the feedback. I considered getting an external tube DAC but I already have a dedicated audio sound card installed in the PC so wondered whether another DAC would be redundant(?).