Honestly, I think you would most likely end up spending money for the sake of spending money. You may get lucky and prefer either the Arcam or the Cyrus, but it would be just that luck.
The Linn Majik (I'm guessing you have the older Majik I integrated amp) was a great integrated amp and so long as it's driving your speakers perfectly well, you would likely have to go a bit higher on your budget to guarantee getting something that was appreciably 'better' as opposed to just 'different'.
Amplifier design hasn't changed a great deal in the last 10-15 years so again, it's less likely that something that is newer will by default be better.
In your previous thread you refer to changing your source by going to a PC based system with a DAC. What did you end up doing in the end?
Your source, in this case, is where you're more likely to find an inherent improvement by going with something more modern. The improvements made in CD replay over the last 10 years has been huge, largely driven by the popularity of PC based music and the subsequent regeneration of demand for external DACs. There have been some really big advances in DAC software and hardware that has been passed onto CD players as well, so that now, for less than £500 you can get a CDP that's at the the same level of performance as a machine costing four or maybe five times that from say 10 years ago.
Finally, buying second hand HiFi is always a gamble. At a certain price point, and it's not very high, the issues move away from 'appreciable improvement' to 'appreciable enjoyment', which goes back to my earlier point. System matching and personal preference are more relevant than getting a better sound and that's more so the case with amps (and it's absolutely the case with speakers) I think that with a CD player.
But, if you've got an itchy trigger finger (and I know what that feels like!) then the Cyrus will have a few key advantages over the Arcam, mainly based around it's ability to upgrade via the PSX power supply that makes a big difference. You also have far greater choice with Cyrus power amps than Arcam if you also want to go down the route of adding a power amp in bridged mode.
