Streamer/dac/preamp with Monitor Audio

Hi all
First time poster, looking for advice on improving my current network player, DAC/Digital pre-amp components with an eye towards a speaker upgrade in the next few years. What I'm really interested in understanding is if anyone has experience pairing the options I'm considering with Monitor Audio speakers and Cambridge power amps (my detailed set up is at the bottom).  

Network Player/DAC/Preamp combo:

• Cambridge Audio 851N (I auditioned already)
• NAD C658 (I prefer blueos to CA's software)
• TEAC NT-505
• Lumin D2
• Mytek Brooklyn Bridge

OR
Network player + DAC/Pre-amp

• bluesound node 2i + McIntosh d150
• other options?

I just auditioned the 851N with the 851W streaming Tidal HIFI and didnt find the sound quality improvement v. the chromecast/HK preamp combo enough to justify the price tag. It was slightly more "open" but at times very hard to discern any difference. I was surprised as I assumed the HK was a clear weak link in the chain.  

No real budget limit but I'll likely buy used, which should open up more options (for example, I got the 851w for a massive discount v. list price)

Current set up:

• Speakers - Monitor Audio RS6 (6ohms, 91db, 40-120 watts). I hope to upgrade my speakers in the next 1-2 years (think MA Gold 200 5G)
• Chromecast audio - toslink into HK  
• Pre amp - Harman Kardon 3490 (two AKM-AK4589 DACs)
• Power amp - Cambridge Audio 851w (connected to HK via unbalanced RCA). BTW, the 851w is a massive upgrade over the HK when i used it as an integrated amp.  
• Sources - Tidal Hifi (non-MQA), GPM, locally stored FLAC
• Room - 13ft wide x 22ft deep. sheetrock walls, low ceilings, low pile carpet. It's a big space to fill.
• Music preferences - electric/guitar driven blues/rock, acoustic guitar w vocals, jazz, some classical
• Usage: 100% for two channel listening

Many thanks for your expert opinions!