Sorry I was unclear. What I meant is DSP like PEQ, Dynamic Loudness, cross feed, tone controls, left/right balance etc, but not the selection of reconstruction filters as this usually is a feature of the DAC IC not requiring external DSP resources.
Only ones that interest me are the Loudness, Bass/Treble, and of course the EQ.
Without having heard the Topping DX3 Pro+, I fully recommend the RME ADI-2 DAC FS.
You can hardly compare the two devices with each other. The functionality of the RME clearly exceeds that of the Topping. The customization possibilities to specific needs are extremely extensive and hardly to be found in high quality hifi devices. This is a real "Pro" device. If you mainly use headphones, the Topping is probably sufficient. But in combination with a good speaker system the ADI-2 DAC plays in another league. The RME is also better adapted to appropriate headphones (high power circuit and low impedance capabilities, e.g. for IEMs). For 999$ this is a very good deal.
Oh and RME offers with the ADI-2 DAC a very simple and meaningful bit test from 16bit/44.1kHz to 32bit/192Khz. Very interesting!
I wholeheartedly agree that the RME is a fantastic device, especially after reading the manual, that does more things than any other Dac/Amp on the planet. And you are correct in stating that it is a good deal for the asking price of $999 for what you get all in one box. Sonically, the Loudness function is by far the most unique and interesting aspect for me followed by the Bass/Treble feature and EQ both of which can be attained through the APO software in Windows.
I think the major aspects that I am not really taking advantage of are; the DSP's (ie..Polarity, Crossfeed, separate EQ for Lt and Rt channels etc..), using high quality 2 channel speakers (i have that in another area of the house), its recording abilities, and probably most importantly its ability to perform standalone without the need for equalization through a pc.
I am just using high quality headphones in my home office that need power from a decent source that is controlled/colored/equalized via the APO software. Previously I used a Liquid spark right off of the PC motherboard that worked well. But my son got that unit and I decided to get something with similar power and a remote that could easily control my powered speakers (Audyssey Desktop Pair) from a distance.
I have to admit that I really love the RME ADI-2 Dac. It oozes pure quality and engineering and build quality while also looking cool. But I cannot get over just how close the DX3 Pro+ comes for what truly fulfills my personal needs for $875 less.