I have used a pair of EVS Ultimate Attenuators Naked between the DNA 225 and my 47 Labs Shigaraki transport and Bel Canto DAC 2.0. The difference between preamp and non preamp is a sense of transparency and yet, there is something that is missing which is body. Body is what some might refer to meat or the preamp gain. If one is to use a shitty preamp, then, you might hear an improvement, but if you had a reference preamp that gives you right amount of dynamics that is clear of glare and also grain, then, the method of going direct might not suit with your ears.