There are actually many options in the headphone market, depending on budget/perference, you just need to know where to look.
If you have a healthy £2k to play with and it were my money, I'd be looking at an offboard DAC for starters. Something like a Meier Audio StageDAC, or perhaps a CI Audio VDA2 are both excellent quality mid-range DACs. Your CD7300 should be fine as a digital transport for now, and I'm not convinced your money would be best spent changing it (unless you want to go with a streaming solution such as a Squeezebox linked to a PC or NAS box...let me know if that option interests you).
Next, amplification. Again, there are loads and loads of options out there to suit all sorts of budgets and listening preferences. Again, my money at this budget, I'd take a solid look at Woo Audio (if you like tube amps), in part because I already have one of their WA22 balanced amps & have been very impressed with it. At this budget you won't want to go balanced (expensive - think of it a bit like bi-amping speakers), and I've heard great things about the WA6SE amp, so you might want to look at that. So many other options too though...if you can get someone to build you a Millet Hybrid amp, they are superb for the money (a few hundred quid tops), and beat just about anything I've heard at that price. Mapletree Audio also make some lovely tube amps (Ear+ for example) that pair particularly well with Grado headphones in my experience. If solid state amps are your bag, Dacs Audio (a UK firm), are making some of the best I've heard. They're mainly a Pro audio company, but I tested a pre-production version of a consumer focused amp (based on their Pro "Headmaster" unit) and it was fantastic. I'd have one the day they are released (not sure when yet) if I were in the market for a new solid state amp.
Headphones. Ideally, again all imho, you want to leave a significant portion of your budget for the headphones. This is not a hard & fast rule, and can depend on the particular components you're looking at (eg Sennheiser HD800s really need great upstream components), but for the most part I think you'll find the best bang for your buck at the headphone end of the chain. Rather like speakers, the headphones will generally have more effect on the final sound that any other component in the chain, and therefore your choice will definitely come down to preference. Unfortunately, this is where living in the UK isn't ideal, as it's quite hard to get a listen to a lot of the stuff out there (applies to amps/dacs as well), and you may have already noticed that most of the companies I've mentioned are based in the USA. So, I reckon with this system you could be looking at spending between £600 and £1000 on headphones. That gets you into the ballpark of the Beyer T1, Sennheiser HD800 (careful with other components). I own a pair of HD800s and they are an amazing achievement...the sound isn't for everyone...very detailed, revealing, neutral...a lot of people like the more emphasised mids of something like a Grado RS1 or the HF2 (if you can find one). Definitely worth looking at the classifieds on the Headfi forum, as they tend to be quite busy & generally reliable.
This is really just a taster...there are TONS of other headphones, amps, dacs, sources etc out there that might suit you better. Really, the Head-Fi forum is the best place to research the whole topic. As a final curve-ball, you may even want to consider a portable rig that you can also use at home. JH Audio are producing some absolutely amazing custom IEMs (in ear monitors, moulded to your ear), specifically the JH13-Pro or JH16-Pro, which have made a lot of seasoned Head-fi'ers give up their big expensive home rigs. If you go this route, you could get a really nice portable source and amp plus some custom IEMs for well within your budget, and of course you can take it wherever you go. Something to think about anyway.
Edit - re your comment about masses of bass...remember, this is a headphone rig, you're dealing with the limitations of small drivers. Whilst some headphones will give you the illusion of a lot of bass, don't expect the earth to move!
Meier Audio StageDAC
CI Audio VDA2 DAC
Woo Audio WA6SE
Mapletree Audio
Head Fi forum
JH Audio