I've probably got useful news for you on two fronts.
Existing modchip
It's probably the original Modchip.com chip. If it is, you can boot DVD-Rs from any region now. You need a JAP high TOC original DVD Game, like Devil May Cry (you can get that in Comoputer Exchange, London). You boot that and when the tray ejects, you swap in the DVD-R of lower TOC. If the DVD-R is correctly burned and lower TOC, it'll work. I did that for a couple of months. Your laser needs to be in good condition for DVD-Rs.
Ideal solution
The origiachip 1.25 is potentially your best solution. (
www.origachip.com).
If you have a 10000 or 15000 (it says which on the back of your PS2) then with this chip installed you can boot import originals (US/PAL) NO SWAP; DVD-Rs and CD-Rs boot using DVD Region X (v1.3 or 1.9( or with AR2 (any version). I recommend DVD REgion X which is free in this month's PSi-2 Magazine
Hope that answers your questions.