Any upgrade ideas?

My current setup(s): 1. Spotify Premium 2. RME ADI 2 DAC FS 3. Stax SRM-D50 4. Stax SR-009s

3a. Hifiman HE1000v2 (powered by the RME)

I’m thinking of throwing another c. £3+k into this - based on your experience, where would the best investment be?

My thoughts:

Option 1: Sell SRM-D50 and purchase SRM-T8000

Option 2: Sell SR-009s and purchase SR-X9000

Option 3: Sell SRM-D50, SR-009s, HE1000v2 and purchase SR-X9000 and SRM-T8000

I would also consider the SRM-700T although I’m not quite sure about the difference against the solid state 700S - more harmonics? (3rd order)

Many thanks.