5.1 under 4k?

It is very simple to know what is 2 or 3-dimensional. I am in audio since 1998. I did listen to many many stuff. I Always test first to know what the properties of the equipment is you test. Wenn you have speakers and an amp which can give a deep stage both. You can test many sources to know if they also can give a deep and wide stage. Wenn a source cannot give a deep and wide stage, the depth and wide is gone. And you have a 2-dimensional image again. It is that simple. Use a source and amp which can give both a deep and wide stage. Then you test many differend speakers, and again you know which can give a deep and wide stage en which can't. I have done these tests hundreds of times. The audio shows with Deftec I never heard a deep and wide stage. Most shops here in Holland demonstrate Monitor Audio with 2-dimensional amps. Most do not understand well how to get it. They also do not know the amps and speakers who can give a deep and wide stage. Even distributers have less knowledge to understand this. At the end it is not difficult to explain what the difference is. I do this comparance now for about 6 years. It works extremly well.

Based on some advice here I traveled an hour to listen to some Monitor Audio silver series speakers. I loved what I heard and ended up taking some speakers home.

I purchased a pair of rx8s, gx150, and a pair of rx1s for surround. I cound not justify the $1200 or afford for that matter for the sub. Can anyone recommend a good sub to match this system?

I like the Paradigm Monitor subs at $600 to $800. Front firing, which I personally like, especially for a carpeted room. Surprising sound in a small package.

Since you are used to Polk, you'd probably like GoldenEar, which is one of Polk's co-founder's current company. At your budget, you could get three SuperSat 60s for L-C-R ($2400), a pair of SuperSat 50s for the surrounds ($1K) and their Forcefield 5 subwoofer ($999). This all comes in around $4400. I've heard their sats with their sub (as well as the Triton 2 towers and Aon 3 monitors), and their products have a *great* folded ribbon tweeter and their satellites with sub sound really good for both music and theater.

The Apex sub of Monitor Audio is cheaper and better then the RX subwoofer. Most other sub's in this price range are a lot less fast in speed than the Apex Sub. I never sell the RX sub, go for the better and less expensive Apex sub. Next step go for an Onkyo Amp. You will hear how much more depth and wide it has compared to the Marantz. Drive and individual focus of instruments and voices is superior to Marantz. Why? Because the transformers they use deliver more ampères. I am surprised you bought the speakers this fast. Marantz can not give a deep and wide stage. That is why it is a 2-dimensional brand.