Trading through an ECN is a good idea, FXALL is probably a bad choice since they have such a small market share. Currenex and Hotspot are both better. EBS (in EUR, JPY, and CHF) and Reuters (in GBP, AUD, CAD) have the largest market shares, but they both are expensive to set up and require monthly fees regardless of how much you trade, their liquidity in pairs where they are not the primary exchange is poor, and their technology is atrocious. Currenex would be the top choice for good liquidity in all pairs (about 10% of overall volume, compared to 5% for hotspot, and 1% for FXALL), execution algos available through their API, and general quality of their technology.
It sounds like you may be best suited to using an aggregator, I would not consider Reuters or Integral and I am not familiar with Apama or Portware. I am familiar with MarketFactory and Flextrade. Flextrade is mature technology and will get the job done. It's a simple FIX api to send orders, and you can write your own algos or use some off the shelf. MarketFactory is newer and from what I know about it it's the best off the shelf aggregator, but I have only seen their marketing material, I've never used the product.
@pedro Banks will only give you tight spreads if they are making a lot of money off you, so it's kind of a mixed blessing.
@assylias Fees are under $5/MM which is less than .1 pips. The aggregate spread on an ECN is going to be tighter than from any single counterparty 90%+ of the time.