Each component upgrade needs to burn both money and time.
My advice is upgrade the DAC module first. I have both the AK4490 and ES 9038.
Their sound signature are quite a big difference. Cost money but minimum time.
Once a while I would change them when I am tired of one signature.
Wonder why Gary not supplying the ES 9038 Pro?
New signalling tubes, rectifier tubes and coupling capacitors may need plenty of burn in time.
Search the net to know more about their burn in periods and sound signature during burn in time.
Since you are going RCA, you could upgrade signalling and capacitors together.
You can burn these new components as spare while you listens to the stock components.
I go for new tubes than NOS. Cost less, no worry about tube life span and easy to replace.
My default is JJ EE88CC, it sounds so much better than my stock 6H6 and EH 6H30 PI.
I upgraded my rectifier last, chose Sophia Aqua 274B, a new design tube in the market.
It gave me to most headache for the lack of info for burn in period and sound signature during burn in time.
Eventually it turn out great after super long burn in time.
Hey, I read the Psvane WE274B replica tube also takes above 200 hours to burn in.
Next upgrade at year end ..... *drum beats* USB board with Crystek.
Wish you a happy journey with MP D2 mk3.
Ok ... now playing Bad Boy, album Primitive Love, Miami Sound Machine