Dan,
To preserve the DTS encoding so it will properly decode you need any copy or transfer to be "bit perfect", which is another way to say lossless, but also implies absolutely no change, including volume level.
In iTunes that means using apple lossless encoding and turning off any EQ or volume normalization, etc. See the apple section of this:
viewtopic.php?f=7&t=154By the way, that mentions apple TV as untested. Only the first generation of apple TV can stream 44.1 Khz DTS. All the later versions resample everything to 48 Khz so won't work for DTS CDs.
Re The DTS-610 ebay is your best bet but it's not clear to me what that has to do with Q8 tapes. You want to encode them to DTS? The normal approach would be to do that in software, but assumes you have a audio interface with at least 4 channels in and a software DTS encoder.
If you want to use the DTS-610 as a hardware encoder you will need to make bit perfect recordings of the SPDIF output. Just at the moment I'm forgetting whether the DTS-610 is 44.1 or 48 KHz output, but you would want to know which before purchasing as if it is 48 KHz you won't be able to use the resulting recording in iTunes. I can check mine.
For DTS encoding in software on a mac, the only solution for less than $400 is here:
http://www.vortexzoom.com/tag/vortex-surround-encoder/but you have to be careful to get the surround encoder (for mac) and NOT the zoom encoder.