The only preamp that I know of does not degrade performance of D90se is Pre90. And Pre90 is not doing much better either. D90se only has 1.3uV(20-22khz no weighting) or 1uV a-wt of noise. If you have a preamp with higher noise, of course you'd be having worse performance.
If you are worry about pop and clicks etc, you are all good to use a preamp.
May I ask
@JohnYang1997, just out of curiosity, what volume control method the D90SE is using?
Like Pre90 is analog, it's probably a ladder-resistor system with relays/multiplexer or similar to make the switching between the resistors. (And possibly using impedance boosting or something in the end of the chain to overcome as much dynamic loss as possible, by making output impedance the same across all volume steps)
Most DACs use digital volume attenuation, which is "lossy". If you turn it reaaaally down, you use some detail, since you are lessening/decreasing bit depth.
There are some other DACs, which use a hybrid solution, by having a couple of larger steps in the analog domain, switched via relays, and compensating the smaller steps with digital attenuation in between. This, in theory, is also lossy", but usually no human ear hears 1 or 2 bits of decrease in the digital domain, ever in real life. (And it's never more than that, since then the relays kick in, and switch to the next bigger step.)
Now the question is, which of these three does Topping use in their D90SE?