You can only buy the 170s on their sight, as far as the refurbs they are ussually just open boxed or returned to store units that denon goes through checks out and sells at a discount, you still get a warranty, and I have bought a few with no issues...
The 170s have an in-home trial period so if you don't like them send them back for a refund....
I thought you were considering used gear? you don't get more of gamble than that, I will take refurbed with a 1yr over used any day of the week!!!
The receiver isnt going to make a huge difference, I recommend the 170s because they are made with top of the line components and I have listened to many bookshelf speakers and I would say in comparison with others the 170s are worth triple their price tag.... You pair them with a good sub like the vtf2 and you will be amazed how warm, clean and defined it sounds... I would get a receiver with preouts so you can run a separate amplifier in the future, the 170s are easy to run but really open up when you have more power, I run 1 of my sets with a small emo miniX, and a wd sealed sub, and I will compare that system to anything under $2000...
good luck with your decisions, keep in mind HSU and Ascend are direct from the manufactuer companies, you get the trial period and you can call and talk to the owner and designer if you like so CS is top notch with both...