The synth in a PSR740 is similar to that in the MU80/100 series but with only 16 parts and fewer voices. If you look in the back of the 740 manual you will see a great deal of sysex. Yhis is not for the faint hearted but you will learn a lot from it.
From the console you have access to three insertion DSPs and one for the Vocal Harmony. All you can do is set the dry/wet parameter for each effect and combine the DSPs in only a half dozen ways. There is also a variation DSP which is only accessible when recording styles. However, when you use sysex via a computer connection, you can use all 5 DSPs as insertion or use the Variation DSP as a system DSP in any combination. This is in contradiction to the manual which is not altogether truthful and is missing a great deal of info. You can apply one or all DSPs to a part or apply them separately or in combination to different parts.
The parts aren't accessible from the console except for the mod and pitch bend wheels but you get full access via sysex. Each part has reverb, chorus, vibrato etc. independent of the DSPs and you can select any of the voices for each part or layer them on to one channel.
There are several ways to get this access, the cheapest being one of the XG editors such as XG Edit, XGGold or XGPad. These editors only give you access to two DSPs and only the XG voices as they were designed for the stand alone synths. The best method is to use XGworks, particularly for the 740 as the XG editor is excellent and will give you access to the whole synth. However, you need my set of updates to get the full capability. I sent them to Nigel but I have yet to find them on the Synth Zone. Maybe Nigel will read this and tell us where he has hidden them. Meanwhile you can find them on Jorgen's website at
home7.inet.tele.dk/js/musik/740pages/ . Look under PSR software.
I use the 'to host' connection to my 740 as my laptop doesn't have a midi port but does have a serial port. In any case, the 'to host' connection is 20% faster than standard midi. Avoid a USB to midi connection as it has poor latency. Maybe USB 2.0 will be better.
Bryan