If there is one thing you could change in your current system. What would it be?

Nothing... or everything. If I suddenly could afford to double my investment... then I would start research. 

Agree with @immatthewj in adding transducers of types. Maybe even immersive audio. 

Small Core Audio Designs ceiling cloud. Arnold the proprietor has a fantastic music room and imo product.

Nothing can improve my system sound. Everything (source, amp, cables, speakers) in my audio system are the best and most transparent sound in the world. Only way to improve my system’s sound will be modify (by me) the expensive (>$10k) SACD player (or streamer)

In 2nd thought, I don’t think that will improve my WT-95 sound because the new chip technology destroys the original musical data and the sound won’t be better. I've modded ESS 9038pro DAC and Chord Hugo2. Anyway, separate DACs can’t sound better than All-in-one WT-95. Every separate DACs always sound veiled and distorted. As long as audio companies don’t know what causes sound distortion, the separate DAC will always sound veiled and distorted. I know why separate DACs sound distorted but there is no way DACs to avoid it.

I won’t mod any $10k SACD player. The sound improvement will be noticeable but it won’t be worth extra $10k. Also, my mod is hard and needs many special replacement parts which are are hard to get for $10k players. Alex/Wavetouch audio

my knowledge of all things audio. That's by far the biggest obstacle in improving my system.