I think looking into better speaker amp is a good idea. SMSL 9 series or maybe a loxjie A30 would fit your build pretty well.
I can understand the need for a sub (although I still think it is overkill), making that a priority is fine. I would still advice you to look into using your mini dsp to alter your bass “level”. You could set up 4 different profiles, first with natural bass. 2nd with thick bass, 3rd with extreme bass and maybe even a 4th with low bass for night time movies or something. Unless you really want to be able to just turn the knob just because you like that idea, you could save money, quality (and a possible headache if you get some kind of ground loops or something).
Good luck!
edit: seems like you are planning on using the internal DAC of your computer? I would advice against that with your budget. Try to get a cheap DAC in there. Also, it seems you have powered speakers so you won’t need a speaker amp. I honestly think an general advice thread for your build would be a good way to start (without using part selector, it doesn’t really work all that well for audio honestly, you can exclude the cables etc). Right now it is still unclear what component is going to do what (for example: I am just assuming U green splitter is going to be used to get sound out of your PC into your amp, but I am not really sure)
For example, if I would explain my system, I would explain it like this:
*Headphones (I have this): *
PC [source]–> SMSL SU9 [DAC] → Singxer SA1 [AMP] → Focal Clear MG [headphones]
Desktop speakers (WIP)
*PC [source]–> SMSL SU9 [DAC] → MiniDSP HD [DSP] → speaker AMP (advice?) → home build speakers *
Active sub also connected to miniDSP (So I can set xover)
That way, people can see what is connected were, and if people don’t know what a singxer SA1 is for example, they don’t have to google it, they will see it is an headphone amp