Power for Paradigm Studio 40 v4

Chrisr....I had the same reservations about buying used equipment.I finally took the plunge here on A'gon and bought a used amp and couldn't have been happier.I have now made several used purchases and have had zero problems.You can find some very nice equipment at ridiculously low prices.The A'gon feedback system is a great help in determining who is a reputable seller.You can also contact sellers directly and ask questions and find out if they stand by their equipment as far as returns if something goes wrong.That being said,I believe you are on the right track by looking to replace your power amp.I owned an Adcom GFP 710 preamp and it served my needs just fine.You need to state what your budget is and you will get better responses.I have no experience with Onkyo but if you are set on buying new check out these authorized NAD online sellers they have great prices.I have dealt with Spearit Sound and the are a great company to do business with.Good luck.

http://www.spearitsound.com/

https://dmc-electronics.com/Default.htm

http://www.saturdayaudio.com/

as a big arcam fan, i'd personally look to change your preamp before i replaced the power amp. i have the alpha 9 integrated, which i believe has a substantially identical amp as your alpha 8, and i've gotten much better results using the arcam's inboard power amp than using beefier (and pricier) external parasound or rotel power amps. lots of experimentation (and lots of good advice on these forums) has taught me that it really is the quality, and not the quantity of the power that's determinative, and these arcams have really good power. on the other hand, i'm not as impressed with adcom's preamps, although i still use one in my office system--they're serviceable but not memorable. i'd suggest pairing the arcam amp with either (a) a comparable-series arcam pre; or (b) an inexpensive passive pre such as luminous axiom or channel island. i sincerely believe you'll be happier with that combination than with the other gear you're considering.

I have had my alpha 8p hooked up to the integrated alpha 8 in a bi-amp configuration for 10 years, and surprisingly, the adcom / alpha 8p sounds better! The all-arcam system had nicer dynamics, no question, but the adcom/alpha is cleaner/more detailed sounding; just more revealing.
The reason why I had to throw away the arcam integrated is because the input selector was not working anymore, only one channel was working, and also, I could listen to a radio station everytime I was depressing the direct button (engaging the tone controls) since it was new. I have seen the delta series (in the 90s) exhibit the same kind of problems. I will not buy Arcam again, especially at 2x to 3x the price of NAD or Cambridge Audio. I really have doubts about the quality of components used.
What scares me with integrated is to have a "cheap", lesser quality pre-amp section, just like in the case of the arcam.
I believe that in the case of amplifiers, we have to look at power and headroom, and then carefully choose the pre-amp for the overall desired sound signature.