As previously stated, regardless of what speakers you choose, you won't see much improvement unless you get yourself an amplifier.. You could go one step further and get a DSP as well. I've used Audison's Bit-ten in the past which was pretty good, and actually pretty affordable these days. but, it all depends what you want from your sound system, and what your budget is.
I've taken your advice 
Having looked at various alternative "upgrade" speakers I've discovered the issue with non-Rover speakers is the speaker chassis is quite a large diameter relative to the mounting diameter therefore near impossible to get anything to fit unless I go down in size or add a spacer, but I'm trying as far as possible to remain original. A bit of digging on the internet and I've found Somerford Mini Spares have new ones in stock! Purchase made 
I was facing the same issue with the speaker chassis not fitting in the original cut out. I used some Car-Audio sound deadening (similar to dynamat, just a different brand) under the parcel shelf board. I also got myself a parcel shelf board from optimise automotive, see here. Its slightly thicker than the original.... So that plus the deadening gave the speakers I choose enough room to clear the body. I went with Focal ES165 K2, which might be overboard, but they sound absolutely amazing, and don't look to crazy custom like some others....
Also for the front, I wasn't a fan of the custom speaker boxes available that fit under the dash. So I removed the air vents.. custom made per hand some grills which i hot-glued in.. I think it came up pretty nice
speakergrill.jpeg 40.44K
8 downloads
Screen Shot 2018-10-23 at 18.23.43.png 469.32K
11 downloads
Edited by leewaa, 23 October 2018 - 04:33 PM.