Upgrade path

Not opposed to replacing the Dunlavys. But most say I'd have to spend more than 4K to do better? I like the detail I get from the Theta just wish I had a little more bottom end. Again most say to get better bottom end I would lose some of the midrange unless I get into super high end amps. So there is my delima. Can I upgrade my speakers or amp using 4K as a budget or at this budget is my only option upgrading my preamp. I was looking at an older Mac amp the MC2500?

Too many variables to consider before throwing out what amp may give you a little more slam. Used to work at the local Dunlavy shop part time back in the days. The SC4s are ruler flat so if your looking for a big fat bottom you may never get there. Your room size has as much or more to with it. We also sold the ARC LS3 and that was a really good preamp but there’s much better today. I’d look at my speaker placement, do you have dedicated circuits to your equipment which your amp really needs to get the most out of it, and lastly if you don’t have revealing cables that can deliver the goods then I’d start there with dedicated lines. The SC4s are big heavy boxes to move around so wondering if you have the spikes in the plinths?

Yes the Dunlays are pretty nice. Not looking for a fat bottom end. Just looking to tie everything together.I will continue to look for a better pre amp... As more than likely there lies the key. Will a tube preamp soften the bottom end? Also any recommendations either tube or solid state for preamps? Would need a pre with two sets of main outputs so I can continue to bi amp.

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.