What are you going to have to give up for the 4B?
I have a 25+ year old 2b that has never, ever, missed a beat...
I can't say that about any of the gear from Sansui (QRX-7500A), Pioneer (PDR-05 and Elite CT-43), Philips (SACD-1000), Toshiba (SD-900), TEAC (Z-6000) that have all died excruciating (for me) deaths way before their time...or even my Adcom GFA-555II that had to have service due to a meltdown it had....
Pair it up with an excellent tube preamp be be prepared to be amazed....pair it with anything pedestrian or mediocre and you may experience the "brightness" that others claim these amps have...it's not brightness, per se, but rather a revealing of all that is fed to it, they are clean and not euphonic amplifiers...if you want euphony you have to feed that to the amp...
I wish mine was a 4b, but I also have played with the 4BSST2 from work extensively and really, really like that amp....