In the DS when not using the attenuator issues without using a preamp are not related to output impedance: they are level matching (can you get as loud as you need for comfortable listening while not hearing an annoying hiss), some amps don’t like very much ultrasonic noise, very capacitive cables can interact with the leakage inductance of the transformer to raise the level of the frequency response between, say, 22kHz and 24kHz.
When the attenuator is used in the DS the last interaction changes to lowering the level of the frequency response near 22kHz instead of raising it.
Still the TSS should help. The TSS has at least 3dB better S/N so any hiss will be at a lower level for a given overall loudness setting. The TSS will default to the “standard” output signal levels: 2VRMS unbalanced and 4VRMS balanced (and with some configuration options 4VRMS unbalanced) which are about 3dB louder than the DS. The TSS will have output level trimming options of -6dB, -12dB, -18dB, -24dB and -30dB instead of the DS’s option of -20dB, this should allow better level matching in more systems.
The difference in topology also has the benefit that the frequency response won’t be as sensitive to the effects of very high capacitance cables at different levels of output attenuation. I.e. the overall sound character and quality won’t change as much when using various levels of attenuation as they do for some DS users.
Still, empirically, lower output impedance seems to help audio quality and so even if the above descriptions don’t explain the relevant effects of lowering the output impedance in the TSS the newer TSS design should help.
This will also allow the TSS to directly drive more styles of headphones directly. I don’t recommend driving headphones directly with the DS or TSS, but still some do use headphones directly and the lower output impedance will certainly drive them better.
I’m sure I’m forgetting some other new benefits 