Hello Lee!
I too have recently become aware of the benefits derived from purchasing a separate DAC. I see that your user scenarios relate to streaming from a PC, and that your goals are to beef up your headphone and powered speakers. The main scenario I sought to improve was quite different, and I'm pointing that out as you do need to hone in on the usage when selecting a DAC, which as you correctly identify as amplification (for headphones) versus not. There are other items to consider here as well, however. If I could I would like to lay out my observations from my quest for a DAC:
* mobile versus not mobile (e.g. desktop) -- I think that your answer is 'desktop.'
* 'Master Clock'-type functionality versus not. This is an area that appears to have become a focus of the latest DACs, so I suggest looking at that parameter closely for your needs.
* USB interface versus 'other' (e.g. Digital Coaxial) -- I think that you're looking at USB, but your scenario above refers to 'mic' out, but there are mobile style solutions that operate on the 'mic' out I believe. I strongly suggest leveraging a USB style connection to your DAC, but that also involves putting some more energy into the 'Master Clock' part.
* separate amplification versus integrated amplification -- here it is clear that you are indicating a preference for integrated amplification for your headset. Again, you may want to look at either a separate amp as part of this upgrade or at a minimum an upgrade path that supports the notion of separate amplification - but my guess is that with only headphone amplification in mind an integrated DAC and amp is all that you need. Your speakers are already powered.
* What music formats are you working with? Right now I'd recommend selecting a DAC based on the latest ESS chips (e.g. ES9068AS) as they support a lot of formats including MQA and DSD 512.
* Are you thinking about integrating your smart phone into this solution? If so then a USB route would again prove useful, and you'll probably want to get a USB audiophile application like USB Audio Player PRO.
* One DAC chip or two? My solution has only one DAC and it seems fine, but there are those who believe that 1 DAC per stereo channel is the way to go.
* Bluetooth integration? for smartphones this may prove handy
* There are other considerations to factor in, but mostly they are 'upgrade path' oriented, and my guess is that you can simply 'start again' if you choose any of these paths as you should be able to get what you need relatively cheaply. Other factors: I2S (a cable interface), Digital Transport (leveraged by I2S), Integration with other digital inputs like a CD player.
My scenario was also a 'desktop' scenario, but my focus was on upgrading the DAC processing on my CD player -- not my headphones. As a result I chose a "2021 Loxjie D30 ES9068AS MQA HIFI Digital Audio DAC and Headphone Amplifier BT 5.0", but the headphone amplification part offers less power than other DACs in this category, so it could very likely not work for you if your headphones are very power hungry. Other brands to consider are Schiit, Gustard and Topping -- they will likely cost more than the Loxjie however.
I've also seen this said in many places so I'll offer this advice too: If you can get a listen to the DAC first, that is a huge advantage. I did not have the benefit of this, but was tremendously impressed by my choice - it has clearly taken my CD player to the next level by not only having a better DAC chip do a better job of digital to analog conversion, but more importantly by 'dejittering' the data stream coming out of the CD player and into the DAC via its master clock. If you ask me the master clock made the most difference on my sound quality and I did not expect that.
Last thought: If you do go for the Loxjie please do not buy it on Amazon. Instead I suggest ordering from "hifi-express" dot com. It will ship from China directly which is where it's manufactured, which may take a while as it involves getting through customs, but it will be worth the wait. I also suggest looking at investing in good cabling for your connections to digital audio input and RCA/analog out (for your powered speakers possibly), if you're planning to use those.
Sincerely,
-KenC