Hi Gferg, please don't throw the baby out with the bath water! The Alpha 10 is a fine-sounding integrated. When it came out it was considered the best amp that Arcam had ever made up to that point. In professional reviews it's sound and inherent virtues were almost always compared to much more expensive amps available at the time.
That being said, and having sold and spent much time with Arcam products from that period, I would make the following suggestions:
1. Source: It may be a long shot, but try to source a DAC-board from an Alpha 8 or Alpha 9 cd player to upgrade your Alpha 7SE. There may be a dealer out there that has one lying around unused as Arcam no longer supports this upgrade. Another option would be to buy a broken 8 or 9 for cheap just for the DAC board. Like I said, a long shot, but possible.
The Ring DAC- derived board from the 9 would be ideal. The Alpha 9 had noticeably more refinement and "air" to it's sound than the stock 7SE and sounds absolutely beautiful on well-recorded HDCD's. I used to demo and double-blind compare the 7SE to the 9 for customers and the 7SE, although a very musical player, sounded darker and not as lively as the Alpha 9 (and later the FMJ CD23) every time when listening side-by-side.
2. Amp: To quote Ryder above: "If more macro-dynamics, transient attack and better layering and separation in music are required..". Exactly, and adding an Alpha 10 power amp to your system and bi-amping your speakers would give you exactly that. Your Castles might suprise you with a depth of bass you never knew they had. The Alpha series of compenents were designed with this upgrade path in mind. You should be able to find a used two-channel Alpha 10P power amp in really good condition for less than $500 either on the 'gon or Ebay if your are patient. A newer FMJ P32 would work fine, too and they are level-matched to your Alpha 10 integrated.
3. Sub: If your particular speakers are not bi-wireable, then adding a small, fast powered sub could really take your system up a notch musically. The smallest Rel from their Britannia series or their little 8" cube might be a good place to start looking.
Just my two cents.. -jz