Your speakers cost £200 each! You were robbed mate! A pair now sells for under £200. You can't always listen to reviews but many of them appear to slate the Pro-jects. Try them with a different amp, they may improve. HiFi is down to personal taste so what sounds awful to one person may sound perfectly ok to another.
You really need to ask some questions in the main HiFi forum. Marantz has a strong following but speakers are a personal choice. I've matched Marantz with Monitor Audio in the past and have been happy with the results, (MA Bronze), many swear by Dali, (Zensor 3), QAcoustics may be fine too. The only way you are going to find the correct speaker for your taste is to audition.
If you've set your budget at £400 just for the amp then buying used might enable you to bag a better amp at a bargain price, just make sure it has an integral phono stage. eBay is good, but used can be a lottery so as always caveat emptor.