When the SUT Route is adopted, the device 'dependent on model' will add a Rich Tone to the presentation, there are models able to impact on the mid's and low frequencies that can have a perception of producing added weight. this can extend, again 'model dependent' to a perception of a Overly Lush Tone where there is a very loose bass and a subdued mid and upper frequencies.
I use two Different Brands Transformers for my SUT's, as each offers a different perception of a Rich Tone, if I want to move away from the influence of the SUT I use a Head Amp or one of the owned Phon's Built in MC Stage.