I thought that rather than start a new thread, this one from a couple of years ago was worth reviving.
I bought a 604 in the summer - it had been a very long time since a bass was in my life, and so I wanted something with a very comfortable easy neck. So I was choosing between the TRBXs and Ibanez SRs. I prefered the TRBX, just. I think because the radius isn't quite so flat - 10" rather than 12". I've been practising multiple hours every day, and the neck has been just as comfortable as I hoped.
How I've got on with the sound hasn't been so smooth - generally, I found it lightweight, tonally.
Firstly, the bass came fitted with Daddario Nickels 45-65-80-100 and I found that there was too much variation in character from string to string. I changed to 45-65-85-105. That helped, but I still had a sense that the character of the bass was best on the E, and got weaker as I went up the strings.
I didn't find anything in the active eq for me, so I took out the battery and felt pleased that I had picked a bass with an active/passive switch. I also found that the neck pickup on its own had masses more character than blended with the bridge pickup, and that even then, I was having to use the passive tone control a lot.
And then I swapped from Nickels to Daddario Chromes (45-60-80-105), and suddenly the bass finally felt like a bass - the A and D strings feel like they're at the core of the sound, with the E wonderfully deep beneath, and the G only a little brighter. The tone control is now not so important, and the sound of the pickups blended has a lot more character.
With hindsight, my mistake was to buy a bass designed to be easy-going and versatile, when all I want is to make a deep, dark, rich tone. I really like the TRBX, physically its very reassuring in its quality, but I think a BB434 might have suited me better, despite being 2mm wider at the nut and 1.5mm thicker at 1st and 12th frets.
Something I'm definitely not complaining about is the looks - always having that dark redburst finish to look at is very nice!