It's kind of hard to comment. I and I suspect many others have never heard of "Guru Junior". Could you be more descriptive?
Arcam and Yamaha are well known and respected.
My opinion on the amplifier is that Arcam makes some of the best integrated amplifiers on the market, along with Musical Fidelity and Music Hall.
NAD and Cambridge Audio also make some fairly good ones, and Marantz is not too bad.
My experience with Yamaha amplifiers has been that they sound lousy and are designed poorly. I would only wish one on my worst enemy.
Were I in your shoes I would return the Yamaha if it is at all possible and get almost ANYTHING else!
I've never owned any Yamaha audio product and most likely never will. However, I know people who do and they are quite happy with them.
Some people are happy with a cheap Yamaha reciver, which sounds like crap to me.
I bought a Yamaha top-of-the line amplifier once, for $800, and it didn't sound very good.
I replaced it with a $300 NAD amplifier, which sounded way way better, and returned the damn thing.