Need some $500 & under Amp recommendations

They look like great deals, those Chinese amps on eBay. Personally, before I bought one of them I would want to know a good technician. At the least I would want his opinion on the build. There is very good gear made in China and I have some of it (Audio Space and Shanling). There is also very poorly made gear from China and it's buyer beware here.

Rather than take a chance, I would choose Chinese-made audio with a reliable North American distributor. The distributor has had his tech check out the gear before he picked up the line. If you do take a chance, though, make sure you know someone who can fix it.

This is just my take on the question, but IMO vintage gear is only a good idea if you are willing to get into the nuts and bolts, and also the history, of the hobby.

You need to know nuts and bolts, and a *good* technician, because older gear needs care: preventive maintenance and repair. It may need modification--volume bypass, preamp out etc.--for some setups. Its value depends enormously on condition and condition is not always possible to judge from appearance. You need to know history because the great names in vintage occasionally produced dud models just like today's makers.

For the OP a Dynaco Stereo 70 after servicing comes pretty close to eating up his budget--a restored and/or modded one could go well over it--and he still doesn't have a preamp or interconnect. I would say do some learning and find out if that's where you want to go, but don't make vintage gear your first step in the hobby, especially for a pair of Atoms. There's time enough later for that.

To me, the NAD C320BEE defines entry-level. It (and probably the 325) is very good-sounding for the money and you can get one for well under your budget. You can tweak it with better-quality preamp jumpers and antivibration feet from Bright Star or Herbie's Audio Lab.

If you need to spend more, the Linn Majik is a very good amp and very convenient to use. It needs the right speakers since it has less power than the NAD. (It also requires Linn's own speaker connectors.) IIRC the Majik sounds a bit more neutral, the NAD being a smidge on the dry and analytical side like a lot of lower-end solid state. If you prefer (slightly) warm and lush, go for a Rega. If I were using Paradigm Atoms a small Rega would be my choice if I could find one.

At present two of our systems use the 320BEE and Paradigm Titans. The combination works for the kids but I'm not so terribly fond of it myself. My GF has the 320BEE with PSB Alpha Minis and that is a better-sounding setup to my ears; the mids are not recessed in favour of the extremes. (Your Atoms may be more balanced towards the mids than the Titans, though.)

At present, you really can't go wrong with any of these models IMHO. You would be happy if you just jumped on the first that came up from a reliable seller. Study the used prices for a bit so you know how much to pay; you won't lose much on resale if you ever need to upgrade.

Yes, I think tubes can sound better than solid state but IME you will need to spend a bit more to go tubes unless you are into vintage. If I were you I'd wait and do some learning first.

As for your clean sound requirement, you will make any amp, and especially the ones in this thread, sound cleaner with a quality source. That's why I would go for the entry-level NAD; it leaves more bucks for the source.

Back in the 70s I used to demo the best speakers in the store using Crown amplification--the IC150 preamp and the DC300 amp. If that's what your father is offering you, I personally would not go for them. It was a long time ago, but I do not remember those units as capable of transmitting emotion, and the amp would be massive overkill for your speakers.