In that case, pretty much everything I wrote goes out the window.
Unfortunately, what you ask isn't readily within the grasp of the unity boost circuit. Unity boost means the un-boosted gain is 1x, and you're asking for a bass boost of only 0.5 dB. This means you have to calculate R4 to give 1.06x gain, which means it has to be 60 ohms if R3 is 1K! Not only is this an ugly duckling in its own right, it then means the parallel bass boost cap has to be ~8uF in order to keep the corner frequency where you have it now, ~330 Hz. If you want to lower the fc, as would make sense to reduce the BB's effect, the cap has to be even bigger. You'll find that if you go shopping for such big film caps, they're not terribly practical, and if they're small enough to fit your box, they're probably not very good for audio.
I'd suggest giving up on your 0.5 dB boost wish, set R3=R4 for 2x bass boost (6 dB), and just adjust the fc to taste by changing the cap value.
To keep your current fc=330 Hz with R4=1K,
you need a cap value of 0.47uF. Doubling that cap value to 1 uF pushes the fc down by half, to around 160 Hz, more of a true bass region.
Such caps are still a bit on the big side, so you might want to set R3=R4=10K instead. That shouldn't hurt the noise floor
too badly, and it lets you drop the cap values by 10x.
There's a middle ground between these approaches, of course. Let's say you end up with R3=10K and fc=150 Hz and decide the boost start point is fine, but the boost level still a bit too high. So, to cut that in half to ~3 dB boost, you'd use R4 = 3.9K and a ~0.22 uF cap.
Bottom line, play with the circuit, and play with the equations. Wolfram Alpha makes the math easy.