Hello!
I have not used the RH450 but I have used an S/PDIF output on a Behringer Bass VAMP Pro (different league, I know) to go into a Focusrite audio interface. The great thing about using S/PDIF (or AES, which is identical S/PDIF but without the copy bit set, so you can route the stream through multiple devices; S/PDIF has a limit to the number of devices it can be passed through) is that you will have a digital format coming out of your amplifier and into your laptop so you will be dealing with a purely digital stream.
I do not know if the RH450 does everything internally in a digital format, but if it does, then there's only one analogue to digital conversion which would be your bass to the amp's internals. In short, this means that there would be less noise and theoretical signal loss due to less analogue to digital and digital to analogue conversions. In reality, you'd struggle to notice it.
If you used DI, you would need to go through another analogue to digital conversion to get it into your laptop. This wouldn't be noisy at all, but best to stay in the world of digital and go the S/PDIF route if you're mixing in digital anyway!
The Tascam has a 96kHz S/PDIF interface, so that would be compatible. According to the reviews on Amazon, a few people had some trouble with it, but in practice it looks quite good for the price. I was tempted by it (and Alesis' similar offerings) but settled with a Firewire interface instead.
Note that S/PDIF can carry two channels of audio down one wire (stereo!). I suspect the RH450 only does mono output, but if you bought other gear in the future that sported a S/PDIF interface and was in stereo, you'd be all set with the Tascam to record two channels with just one lead, in crystal clear digital.
You are barking up the correct tree. The 96kHz/24bit sampling is far superior to CD quality, so you'll have to downsample it for your CD listening chums; Logic will do this I think.
Cheers
Rich