Upgrade path

It seems like you're overall happy with the sound you're getting but just looking to augment the bottom end a bit.  That seems to be common with your speakers and what the SC4a may have addressed.  I doubt spending $4k on speakers, amp, or pre is going to get you what you seek without potentially compromising other areas.  If I'm you, I'd demo a sub with a good bass management system and see if that adds what you're looking for.  If that helps I'd then get a second sub and live happily ever after -- although I'd eventually replace the preamp as well.  Best of luck. 

If if you have the room: bigger Dunlavys,...or sub-woofers.

Thanks Soix, and unsound. One issue I do suffer from is that some tracks sounds mediocre in my system. others are a sonic bliss. My guess is that its the track/recording itself. Thought switching one of the 3 pieces out would give me more of a even tone across all my music. Also with the Dunlavy speakers Prior to getting the Dreadnaught amp I was running a set of Emotiva mono blocks 500watts while not the greatest of amps but they were good and controlled the bottom end of the Dunlavy's very well. I like the Dreadnaught a lot better. Night and day difference on Sonics and presentation, detail, and midrange. This is what gave me the thought that a higher wattage amp in the same league as the Dreadnaught or better would give me the total overall package??

Would love some bigger Dunlavy's but only have 4k to play with bigger Dunlavy's have been running 7k as of late..

Keep in mind the value of your current Dunlavys.
Others might disagree with your power observations with Dunlavys, but you might(!) be on to something. I had a friend go from two 200 watt mono amps to four identical factory matched of the same amps, and the improvement was much greater than either of us expected with his SC IV's. I'm still not sure whether it was the extra power, the longer Class A bias, or some combination there in. 
The SC IVa' are capable of more of the things you are seeking than you might think. Unfortinately they don't show up on the used market too often. The SC V's show up more often and usually for less than $6k, so with the sale of your IV's you should be within budget. One caveat: a lot of V's and VI's were used in recording studios and might have seen a lot of (ab)use.