Tube DAC Recommendations


I am in the market for DAC; my preference is a tube DAC. My primary music source will come from a computer or music server. The DAC will connect to Sim Audio 700i integrated amp. Budget is up to $7000 for the DAC.
I have been studying this forum over the last several months but cannot seem to find a consensus on the top 3-5 tube DACs.
Any input is appreciated.

Thanks
ddelisle911
To all-
Thank you for your responses; I welcome more. In the meantime, I will start my research on the above that were already mentioned, I now have a starting point and this helps a lot.
here is another opinion:

first, i have been attending ces exhibitions for fifteen years. i have also attended many shows in nyc. from those listening experiences, i would try to find the original zanden dac, not the current version.
You may want to consider the Concert Fidelity DAC.A used model is well within your stated price range.It`s exceptionally natural with wonderful tonality.
Regards,
It seems to me that tube DAC technology may not have caught up with the current sampling rates currently on the internet.
Perhaps there is a limitation of hi rez music available; I will need to check that.

Two of the suggestions above have limitations regarding the sampling rate. I have no CD collection right now; I am starting from scratch. The plan was to use downloaded hi rez files from the internet and store this on a server. My thinking was that I would get a better sound quality.

I am not opposed to making an investment in cd's; I just thought that I was going backwards with CD's. Your thoughts?