I came across this player, to be released soon:
http://us.marantz.com/Products/3223.aspSeems like it might make for a good tube output stage candiidate, esp due to the three digital inputs (including USB up to 24/96)
It should go out the door for maybe $400 less than the Sony 5400, and with the ability to use as a DAC as well as SACD, I'd think that your tube output would just be

Dan, any experience modding Marantz? I have no idea what the internal layout is, which i guess could be a deal breaker...
-Mike