What is the best thing for me to upgrade next?

Hi all, slowly working on upgrading my system and could use some advice on where to put my money next!

I only have 1 line level audio source - a streamer and that’s probably how things will stay. I’m not interested in amassing a collection of physical media. All of my music is stored lossless on my NAS.

Here’s where my audio chain started:

Phase 0:
[Source: Sonos Connect] > [DAC: None] > [Amp: Bose Lifestyle] > [Speakers: Bose Acoustimass 3]

I recently replaced my speakers. And I’m now using an amp that I had in storage that I intend to ultimately replace.

Phase 1: (now) [Source: Sonos Connect] > [DAC: None] > [Amp: Harmon Kardon PA2000] > [Speakers: B&W 805D3]

Phase 2: (next)???

So where do you think I’ll get the most bang for my buck once I recuperate from Phase 1 and am ready to buy the next things?

Do I save up to replace my amp next? Thinking something like a McIntosh MC302

Do I put a DAC between my streamer and amp? Thinking something like a Topping D90 or something from Matrix Audio (Element X / X-Sabre Pro, etc.)

Or replace the streamer? Not sure what yet, looking at Aurender, Node 2i, Sonos Port, etc.

What are you thoughts on where I should go next once I recover from the speaker purchase?