Don in Tennessee,
Jb8312 has some good advice. I would improve your system one piece at a time, listening to and enjoying the new piece until you yearn for something new. I tend to think you want to start with the source first for two reasons:
1. you can't add information back that didn't get off the record or CD to start with, and
2. Technology has improved the most in CD players and turn tables over the last 20-30 years compared with amplifiers and speakers.
Your current receiver and speakers will do more with a better signal than a better amp and speakers will do with the HK and Dual IMO. So I would decide which you prefer to listen to the most, vinyl or CDs, and make a major investment there to start.
For a CD player, there are sort of three tiers in the sub $1000 range for new players: $300-$500, $500-$750, and $750-$1000.
In the $300-$500 range, I would look at the NAD 525BEE and 542C, the Cambridge Azur 340C and 540C Version 2, and the Music Hall C-25. These will all provide noticeable improvements over the HK multidisk changer. The Music Hall is probably the best bang for buck even if it is at the higher end of this range.
Moving up to the $500-$750 range, I would listen to the Cambridge Azur 640C Version 2, the Rotel RCD-1072, and the Arcam CD73. These players are a step up from the other batch in terms of resolution and timing, and start to take you into the edge of real hifi. Significant improvements generally cost a lot more...
Which takes us to the $750-$1000 range, where I recommend the Marantz SA8001 and the Rega Apollo. These are fairly sophisticated players that are probably starting to get to a point where their potential wont be fully appreciated with the amplification and speakers you currently have, but they will provide building blocks to carry you to the next level.
You will probably be able to find almost all of these players used on here or on ebay (at a steep discount) at some point in the near future, and that may be the best way to go, particularly if you live in an area where they are difficult to audition in a store.
No matter which unit you go with, I would invest in decent interconnects to hook it up to the Marantz, spending 10% to 20% of the value of the players on good wires - so, between about $50 and $150. people may tell you that you need an after market power cable too, but I would cross that bridge later.
For turntables there are great tables available new starting at about $350 and going up in basically continuous fashion to the price of a small house or tournament fishing boat (hey, its analog right?).
At the lower end (about $350-$450) for a table that will provide a significant step up in sound from the Dual, I would suggest a Pro-Ject basic or Debut III, a Rega P1 or Thorens TD158 or Music Hall MMF 2.2. These will probably come fitted for the asking price with an Ortofon or Goldring cartridge that will work very well.
The next jump up is to tables costing about $600 to $700 with cartridge mounted. Recommended models include the Rega P2 with a Rega cartidge, the Thorens TD190 with an Ortofon cartridge, and a Pro-Ject Expression III with a Sumiko cartridge. These will provide more of everything and cleaarly eclipse the Dual you are currently running in terms of quietness, timing and insight into the music.
The sub $1000 category is full of great tables that start to hint at everything the truly great audiophile tables can provide, but just giving you a little less of it in every area. As with the higher end budget CD players, these tables and cartridges will be overkill with the Marantz Receiver and the little Athenas, but they will make your current system sound much better, and hang in there as you upgrade other components over time around it.
-Music Hall MMF-5.1 w/ Goldring cartridge
-Rega P3-24 w/ Rega or Ortofon cartridge
-Project RM5 w/ Sumiko cartridge (HO MC cartridge, may not work well with Marantz)
Good luck.
