Which makes the biggest difference?

I’m just referring to digital playback here.
I forgot to mention source, such as streaming or spinner.

DAC. Just remove the preamp. If it's better SQ it's a crappy preamp not worth consideration.

Well, yeah, the traditional analog electronic components truly get your system up 'n zooming. But when it comes to collecting and translating those digits into stuff the old school gear can recognize, for me the DAC brings to bear the biggest difference. Heck, my DAC even makes the YouTubes that come off my laptop sound pretty good.

On my difficult to drive speakers the 4 amps I have had on them made a difference. It was not huge but on certain music the more powerful amps at 2 Ohms made a difference. I could also tell the sonic signature of the amps but that difference was not huge.

I have had a few DACs in the house, tube, warm SS, and neutral SS, and they made a smaller difference. The tube DAC softened things up while the SS amps were much closer in sound. When I added a Convolution filter for my very revealing headphones I could not tell the difference between the 2 SS DACs. The filter worked mostly on shaping the high frequencies. I also think DACs are of very high quality these days, with most sounding very close to each other.

The preamp I now use, a warm and detailed piece, made a huge difference over the very neutral preamp I way using before. Especially so in the bright headphones I use.

When I switched from Ethernet to Fibre Optical streaming I had the biggest jump in performance. It was not even close in my setup.

1) Streaming
2) Preamp
3) Amp
4) DAC

BTW - A preamp ALWAYS improved the sound in my setups. One of my DACs also does not have a volume control (a feature in my opinion and not a deficiency)

When I switched from Ethernet to Fibre Optical streaming...

Than you. i know the local ISP ran Fiber optic cable throughout the city/town where I live but hadn’t thought about it within the house. I didn’t know it was available. Now I do and will check further.