I replaced my Monoprice SW-10 with a Klipsch R-120SW (the SW-10 was buzzing.) It's a little deeper and clearer with the bass, which is nice. I'll eventually drop more money on a better sub in the future. Overall, I'm quite pleased with the set-up as it is.
I still stand by my initial...
I might spend a couple grand on a Marantz receiver and a matching CD player in the future. My space is rather limited, and I have other hobbies that also cost a fair amount of money (guitar, TTRPGs, computer games, etc.) For now, I'm quite content.
I bought my Denon DM-41 a couple years ago. It's a fantastic system and it sounded amazing out of the box. Like everyone else here, I got bit by the upgrade bug. Since the DM-41 is relatively low-wattage system, I wanted speakers with a high sensitivity. Naturally, this lead me to the...
Most people seem to recommend the Apple Dongle for connecting wired headphones to their phones. I went with this one from Anker. It feels way more durable, looks great and sounds great.
Thought I'd put it out there.
Anker makes a good one, if you don't need any extra power. The Fosi Audio DS1 is a pretty solid choice, and you can get it for like $60 new on Amazon (it can drive most common headphones, even if they're higher impedance.)
I have a Denon D-M41, WiiM Mini and a Monoprice SW10. When it comes to headphones, I like my Audio Technica ATH-M50x's and my Roland RH-A30's. My total investment in that is probably around $1k. Overall, I think it all sounds fantastic.