So I have a TC RH450 and its a really great amp. The features are stupid good, and everyone I show it to is like "it does what?!"
The issue I guess I have is the RH450 is voiced a lot like the warmer vintage-y feeling tubed bass amps. It sounds great, but I'm becoming more and more convinced it's not "My" sound. I really dug the SR 1206 I had going through it -- It had some Nordstrand Big Singles in it. Bright and lots of clank. But when I got my Yamaha and my fretless, both have a lot warmer sounding electronics. I was thinking about flipping the 450 to get something more modern sounding and brighter sounding. Unless there's a way to get that sound from the 450 and I just haven't discovered that arcane knob setting yet?
For reference, I really like some of the GK tones (Tried out an MB200 the other day and I really liked it) and I have always really liked the bright punchy sound the new Acoustic brand bass amps get.
I think MarkBass is 'the one' for modern sounding amps. I play a Hartke and am very happy with that, but for some reason they don't sell as well as the GKs. I am really happy with mine though - it is extremely versatile and very clean/modern. Victor Wooten plays them, but he uses EMGs as well. ('More Modern' than that is a stretch IMHO) I used a GK 20 years ago for synths, and it really did sound great; bright and warm and wonderful until it died in much smoke in a bar in New Rochelle (I banged some Pat Benatar looking chick and her best friend together that night, and I wasn't even the singer! LOL)
I hear very good things about the new recent GKs though, as I do the recent Carvins, but MarkBass is the one I hear about the most. I haven't demoed many Marks because of their high price, but if you are selling to buy it might be worth checking them out. But 'modern' usually means 'jazz clean', so there's that too. If you are looking for a rock amp, the Mesa Carbine is supposed to be the shit, up down and sideways, but I haven't played that one either, sorry Ken.
Maybe....if you are (were? sounds like you don't have it anymore) digging the TC you have with the SR, you should consider the pre's in the Yammy and your new fretless? Might be cheaper to swap the pre's in the basses than the amp. 2 new 3band Auderes could run you under 400, and more like 300 used BEFORE you sell the pre's you've got in your current basses.