Adding speaker wire

I am redoing the stereo in my 2013 Tige. It came with a basic 4 speaker stereo with no amp. Clarion deck and 4 WS XS-650 in boats. I am adding an WS Ht-6 for the inboats and to drive a WS sub. The existing speaker wires are connected to the deck and won't be long enough to get to the amp wall which will be directly below the current deck. So I need to add wire to get to the amp. Probably 2 feet at the most. Can I use a high quality(Uline/3m) shrinkwrap butt connector to add wire? I know soldering is probably best but the wires are wrapped in a loom under the glove box inside the observer seat compartment so its really not practical. I can barely crawl in there and the thought of trying to solder in there isn't pleasant. I know the butt connector will work but will it effect the sound quality. It would be just for the XS-650's which will be getting roughly 110 watts each.

There's no issue with using butt connectors. I put a little CRC marine dielectric grease inside each connector prior to crimping it. Make sure and give the connection a little tug after your crimp it to assure its crimped well.

You probably won't have to extend the wires for the rear speakers.

If youre adding an extra two feet, I would add a bit more then pull it back to where the speaker is. If you ever want to replace your speakers or take them out for any reason, if you have no slack behind the speaker hole, You have to disconnect the speaker wire from the amp and cut all your zip ties before the speaker comes out.