Hi Mitul,
I am sorry I could not call you or write any earlier. Just got home from work. If you want to discuss, I will give you a call some time tomorrow, and I will write my impressions right now.
The Arcam FMJ CD 23T is not one of their current players (the current ones are FMJ CD 17 and CD 37). So you must be considering it as an used piece. In its day (2001-2004 I think) it was regarded a very very good product and cost about USD 2500 or thereabouts. It was reportedly very very detailed and at the same time smooth. This CDP was built when Arcam already made a name for themselves for making CDPs from ground level up. Unfortunately I do not think I ever listened to this particular player, but I have heard a few of the Arcam CDPs and I sort of know their house sound. Some people BTW find the general Arcam sound a bit bland and un-involving, a matter of personal taste, I guess. Arcam is known for clean sounding electronics, but you may not get a lot of body and dynamics, but that's only a very general comment. I hear that the current CD37 has broken the trend and sounds a bit different and more exciting, but again I have not heard the CD37 either. The most recent Arcam CDPs (discontinued perhaps a couple of years ago) I have heard are the CD 192 and CD 73 (from the Diva series). Both of them are very decent players with the 192 clearly the better and much more expensive one. One thing for certain, an Arcam would never be offensive in the audio presentation, they would always produce a reasonably balanced and 'polished' kind of sound, for the lack of better words.
Cambridge Audio is known as a budget brand and they have VFM image at a lowish cost. However, their 740c (around USD 1000) and 840c (USD 1600) are wonderful products at the price point they go for and perhaps a bit more. I own the 740c and have heard the 840c. There is a serious difference between the 640c (whichever version) and the 740c/840c so much so that you may doubt if they are from the same brand. Some people may not like them (I mean the 740c and the 840c) because of the image of CA as a brand, but I know very few people who have actually given these CDPs a serious listen and not liked them. I have paired my CDP with an amp which is a few times the price of the CDP, and equivalent of my speakers (very old) would be many times the cost of the CDP, and I am happy, because compared to many systems I have heard in the last couple of years (some with quite expensive transport and DAC or CDP) I do not think I am missing that much. It also could be that my listening ears are not good enough or I am plain simple biased. But I am giving you my honest opinion. I am aware that as a budget brand, all their components are not of audiophile standards, for example inside the 740c cabinet some of the opamps and caps could be improved very easily (and some day I'd mod these up), but it has a good power supply, a reasonably reliable transport for the price and 2 good Wolfson DACs (8740), and of course a good upsampling design (24bit/384kHz). The 840c employs a very similar, if not the same, design with better components (DACs are different) and balanced inputs.
The rest of the system is equally important because synergy cannot be ignored. Synergy is not a cliched stuff.
Sorry, got dragged away by my wife for dinner at this point

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Anyway, your amp and speakers have to complement the sound your source is producing. My advice would be to audition these CDPs (both the Arcam and the CA 840c) with your amp and speakers and see if they sound satisfactory to your ears. I have done a bit of experimentation with my CDPs positioning (isolation is a big issue with all sources) and have given a stable power source and good power cord with excellent connectors.
To cut the long story short, listen to both CDPs in your system. The Arcam is an established mid-level CDP, but it is got to be an used piece (given the model no.) and see if it's reading CDs properly and what is the asking price. On the other hand, CA 740c/840c CDPs despite their budget brand name and budget/midlevel prices are a bit better than their prices and image may suggest (keep in mind there is huge difference between the 640c even if it uses the same DAC chip, albeit only one, and no upscaling). if you treat them respectfully, that is, couple them with good amp and speakers, give them a good base, good interconnects (I have experimented a lot from silver cables to the run-of-the mill copper cables) and power cords, they may just satisfy you.
Regards.