CAL Audio used to offer their customers resistors to use in their Alpha DACs. Those DACs had 3.5V output instead of the regular 2V for the purpose of bypassing preamp. But, if the customer wants to use a pre, then they can solder the resistor in the DAC and reduce the output voltage to 2V. You might be able to find a similar resistor for the Tjoeb.
Regarding your original question, I don't think you will get the "tube" experience simply by using the tube drive stage in your CD player to drive your amp. When I had the CAL Alpha, it did have a few of the tube's sonic attributes and is present regardless of it being connected to pre or direct. So, from my experience with the CAL stuff, tube output stage is vastly different from having a tube preamp.
Regarding your original question, I don't think you will get the "tube" experience simply by using the tube drive stage in your CD player to drive your amp. When I had the CAL Alpha, it did have a few of the tube's sonic attributes and is present regardless of it being connected to pre or direct. So, from my experience with the CAL stuff, tube output stage is vastly different from having a tube preamp.