The DSO8064A/MSO8064A/DSO8104A/MSO8104A uses the same acquisition board. That being said, they are way more expensive then the 54831M. All the 54831M, 54831B, 54831D, 54832B and 54832D also uses the same acquisition board.
The first thing I would try before ordering anything else is to find the real issue. As had been said, when the 50 ohm doesn't work, it's usually blown. One test I would do before ordering any part is measure the input impedance of the faulty channels. I agree with Ovidiu and Amir, 99% chance the input termination is blown, but I would verify it first. You can also follow Keysight calibration procedure. Usually, in the service manual, there is a flow chart that links a specific failure to the hardware issue.?
Keep in mind that a 54831M is worth about 700USD (even though seller are selling twice too expensive), so before spending 200$ for replacement parts, I would look carefully at eBay listing. I bought mine last year for 800USD with probes and it passed all self test and self cal.
When you say the calibration fail, does all channel fails or only the 2 faulty? Because if all channel fails, there is a second issue somewhere.
The other thing is your OS. I don't want to say it's impossible, but... Changing the OS in any of these product is extremely hard, even more with these older units. Windows95 and Windows XP works on totally different architecture. The only thing that could help you is the 54832B had a windows XP version. If you can find an image of a 54832B image, it could work. There is a big step up from W95 to XP, mostly for the USB drivers, but the step from XP to W10 wouldn't give you much. As suggested, one of the best upgrade you can make is to use an SSD instead of that drive.?
If the OS is a major concern for you, I would look for a DSO8064A instead.
