Adcom gfa 555 or 5400

Hi, new here and new to the stereo hi-fi world. I'm looking to get my first separate amp to run my two front speakers off my Denon 4400 a/v receiver. So did some research and heard good things about Adcom, and their prices seem pretty affordable for a beginner. I have a chance to buy either a 555 or a 5400 both for about $300. My speakers are Monitor Audio silver 8's. The 555 has been with the seller for ten years and he says its running great, while the 5400 is being sold by an audio technician and he claims that he's just serviced it and that its also running great. I'm not looking for booming bass....just a nice warm clear sound from my two front speakers. Can anyone point out the cons/pros between these two older Adcoms, I know that the 555 has more power, but I'm more interested in the musical aspects of either amp. Cheers and thanks!
My experience with Adcom amps is kind of dated (late 80s to early 90s) but I did have access to their line as a salesman and purchased several models on accommodation during that time.  My memory of those two amps specifically are, the 555 had good power, decent sound stage but somewhat limited air around musicians on stage, upper mids into highs tended to get a bit bright when asked to open up the volume.  For all that power, I always found myself turning it back down to tame the edge that would start to appear and this was on many brands of speakers.   The 5400 came a few years later on, still had a few pairs of the speakers from the first go-round with 555, 565’s & 585-SE.  The 5400 seemed well balanced, smoother mids and highs with less grit or sizzle, sound stage was admirable for a budget amp with better spacing around musicians.  The only slight down side was the bass when volume was elevated enough to demand more control and reserves.  This is where the 5400 would run out of gas compared to the older big block style amps.  
I don’t listen anywhere near as loud as I used to and if given a choice between those two amps now I would lean on the 5400 for a more musical presentation.  
I had a 535, a 545, and a 555. I thougt the 535 sounded best.  Im not so sure though that Adcoms are going to pair well with your monitor audios though.  The sound may go to lean and bright...

I fried my 535 by accidentally touching the positive and negative speaker wire leads together while the amp was on, by the way.
I always felt that B&K amps, especially the reference ones, to be the best sounding / bang for the buck amps in that $300-$400 range.

I’d look at B&K, Parasound and NAD amps in that price range too!
Thanks very much guys. Looks like I can get my hands on a parasound hca 1000a for about the same price. 
I had the 535 paired with the 400 (which I still use as a phono pre-amp and radio).   I more or less agree with the previous posters. At first I heard plenty of detail I wasn't used to w/ my old system, but then "lean" "too bright" "sizzle"--whatever. A lot of my music (particularly voice/choral) became unlistenable.  The best thing about that amp was that it inspired me (in some desperation) to try out an entry level tube amp, which I have been using ever since.  I gave the Adcom away.
I kept my 535 because it's not worth much and still sounds better than a receiver. I don't have a receiver, but if I inspire a friend to jump ship and go more toward audiophile gear, it's an easy re-gift! Good luck, OP!
Thanks everyone ended up grabbing that parasound hca1000a for $260, so didn't have to choose between the adcoms, the parasound is sounding good, very "clean" sound and it's running very cool, looks like it's running my silver 8s easily
A while ago, I'd say the same about the 535. But I had it modded by Hoppe's Brain, and wow, what he did with it. New transistors, caps, resistors, and more. I've had Parasound, Naim, Van Alstine modded Dynaco, a couple more amps. Until I have a few thousand to play with, it's my keeper. Unfortunately he's experienced some physical problems such that he doesn't do modifications anymore. He will sell you his boards etc for you or someone else to put in 535's and 555's. (btw, I have no affiliation, just admiration)
The choice of an amp should depend on a few important factors, but most commonly those are compromised in favor of price.  My first big amp was price first and I regretted it as that dog of an Emotiva would add sibilance and bloated bass when neither was in the recording.  

Anyway, I've owned the Adcom 5400, Parasound Halo A21 and presently have a current production Adcom GFA 565SE, which is a different animal from the decades old 565.  And a few other amps along the way.  The current production Adcoms are very competitive  soundwise, if you don't need bling or jewelry.  

You need to know what kind of sound you prefer, what the sound signature of the speakers is, and whether an amp being considered will have good synergy with the speakers and move you towards your favorable sound signature or not.  Frankly, it's a roll of the dice to expect strangers on the internet to know your preferences, and room acoustics well enough to give any advice beyond general tips. 

These days, I'm reluctant to buy a 20 30 or 40 year old  amp because they are nearing end of life, or major repairs.  YMMV, but with new amp prices dropping while modern technology gives better SQ and build(at any given MSRP) and lower prices(unless you want the bling factor and boutique brand parts), it's often best just to bite the bullet and buy new, or recent.

Thanks 213runnin that was very insightful.  I'll start looking at some newer amps then as I get used to the parasound and maybe move on from it at some point in time. 
Go with the 555 but make it the older version which sounds substantially better then the newer version that came out afterwards . 
If you want ‘warm’, I would look for something other than Adcom. I had an old Adcom 545. Yes, it was good, but not what I was looking for. I sold it and bought an old B&K (in your price range) and was much happier.

But, what you might really want to consider as well is a separate preamp with an HT pass through. AV receiver will not provide a good stereo experience. Been there, done that. After I got a separate amp (current Belles) and a preamp with HT pass through, it made a tremendous difference in sound quality for 2 channel listening.
Any suggestions for a decent preamp with ht pass though? Something used or older would be fine, I'd like to stay around $300 or under
Parasound Zpre3 punches way above its weight IMO. You can find them for about $350 if you search around.

That amp you found looks like a solid choice, and I’ve heard that the Zpre is good bang for buck.  As long as it has the bypass.
 Good luck with your search.
The Parasound Zpre has HT pass through.

call Safe and Sound, they sometimes have it as ‘b stock’ for about $330
The current model Schiit Saga+($399) and Freya+($899) have home theater bypass. It is a free feature all of their preamps have. I recommend the current model preamps because they shut down the tube buffer when it is not being used. Instructions at the bottom of the page:

You simply select the input, put it in passive mode and turn the volume all the way up. Instant 1:1 home theater bypass with only a relay in the signal path.

I realize that the Saga+ is a little out of your price range and the Freya+ is way out of your price range. Part of "saving money" when you are just getting started out is sometimes buying the right product the first time around. Buying something that serves your current needs AND your future needs can save you a lot of time, money and headaches in the long run.

Before you buy a preamp do some research and explore the advantages of having XLR inputs and outputs available to you. Balanced is the way to go if you want better sound quality and compatibility with more equipment.
For what it's worth, I had a long conversation with an experienced speaker designer, and he really likes the Parasounds (including the small light NewClassic 2100) as well as the Hint 6 (more expensive) and the stuff by Belles. He is really happy with the Van Alstine SET 400. FWIW. 

B&K were mentioned a few times. What models fall into the 5400 and 545 price and power range?