Stellar Gain Cell DAC , RME ADI-2 or other with Node 2i?

I’m considering using an external dac with my system currently composed of :
Odyssey Kismet in Khartago amp
Ascend Sierra 2 EX 
Bluesound Node 2i
Rel S5 SHO

I’m streaming through IPhone via Qobuz and Deezer Top tier and don’t really think that I will ever add a CD player or turntable but you never know. 

It it seems that my prime candidates are a used PS Audio Stellar Gain Cell Dac or RME ADI-2 at this time. 

Both of these feature preamps and I think that down the line I will probably add a tube preamp (possibly a Odyssey Candela?) as funds allow so , they may be overkill? It seems to me that at the (relatively!) low cost of those Dacs that a preamp would just be a plus anyway? 

Should I prioritize a tube preamp before getting a dac or visa versa? Should I even get a tube preamp? What about upgrading to a Blueline Speakon for the sub and/ better power cords first?

I listen to all kinds of music btw.. 

Thoughts? 

Also, what would be the best way to connect everything anyway? I have Groneberg interconnects from Klaus but they didn’t fit the Node 2i. Would they work with those Dacs? 

Thanks!