I find the HD600 to sound more like the T1 then the HD650 does. The HD650 has too much bass and not enough treble to be similar. The HD600 has many similar qualities to the T1 (smoother, full, and detailed). The HD600 would actually be warmer than the T1 but still it's a much better choice than the HD650. The HD600 is not that power hungry and an OTL amp could power it perfectly.
The Taboo is a nice option but I would only recommend it if you were interested in cans like the HE-500 or HE-6. The T1 and HD600 can get by with out 100mW-200mW, so having 6W on tap is a bit much for them.
HD 600 would be closer to a T1 sound than HD 650s, another option to consider would be the K701 or the DT 880, although they have less bass than the hd 600 i think.
the HD 650 sounds nothing like the T1, completely opposite because the HD 650 is dark and has a much warmer sound with less treble emphasis.