D’Agostino amp with Spectral preamp

Pre-2k ohms,  amp 100k ohms

How do you know if that is a match or not

Spectral recommends that its amps and preamps be utilized together. i agree with Audiotroy in that mixing Dag and Spectral will get you the worst of both worlds. Go all Dag or Dag amp with tube pre, a combo I have heard in my home which I thought was fabulous. Spectral is fast and clean. If you like that, go all Spectral. Anything else will ruin its presentation, not complement it.

1++ Spectral has a weird or rather very different way of designing its stuff and should only be used together. Although it is not death to use a Spectral preamp with a Dag amp you will need another preamp in time as you plan. It is death to use a Spectral amp with most other preamps. A friend fried his amp this way. He returned it to Spectral for repair and they asked him if he had used it with another preamp. He had not told them what had happened. Consequently I do not bother with Spectral Gear. It is great sounding stuff used correctly and very well made but I also lean to the warmer side of things.
Daniel D'Agostino is not someone you want to buy anything from. When a potentiometer in a 7 year old Krell preamp (this was way before he left Krell,) went south he personally informed me face to face at the NY show that the potentiometer was a custom device and he does not stock them and he is not going to have another batch made. He recommended getting one from Radio Shack and mount it to the top of the preamp which was a very slender unit thus the need for a custom pot. The marketing literature said "Built to last a lifetime." My ass, gold screws and all. Most people buy his stuff because they are impressed by the looks. I personally think his stuff looks silly. Don't waste money on gold screws. It is the stuff inside you want to spend money on. 
If you like the warm sound go with PassLabs. If you like the sterile, clean sound go with Boulder. I'm sure there are others that are fine also but I have experience with these two and I can vouch for them. Both have great service and back up their stuff even after the warranty is up. 
When one of my Krell KMA 100s finally toasted its output stage at around 20 years of age I gave them to the friend of a friend who though he might be able to fix it for himself. They were wonderful amps and the very last D'Agostino products I will ever purchase.