Motorola Inc. reportedly has several potential suitors lined up for its set-top box division, including private equity firms and cable hardware company Arris.

This is the latest break-up rumor to launch re: Moto, ratcheting up a feeling that the company would be better off spinning off a unit or two, or breaking into two or even four parts.

Reuters is reporting that non-binding letters of interest to bid on the STB division are due Wednesday, with Bain Capital, TPG Capital, Blackstone Group KKR and Silver Lake Partners among the interested parties.

Motorola is “a combination of four business entities with no synergies,” said analyst Pierre Ferragu of Bernstein Research recently. Of those businesses (home networks, wireless infrastructure, enterprise mobility, and the handset unit), the handset division is the most obvious target for a spinoff, struggling mightily in the revenue department in the wake of the iPhone onslaught. Selling it off was the plan until the idea was put on the backburner about a year ago, following signs that the division could be salvaged with the right mix of form factors (Android, specifically) and cost-cutting.

Last month, the Wall Street Journal snagged inside info that Motorola was looking to sell its profitable home unit, which recorded $10.1 billion in sales for 2008. The gear-maker would take a mere $4.5 billion for it, sources said.

Ferragu noted that each division would generate more value on its own. He fingered Ericsson and Cisco Systems Inc. as potential buyers for the wireless infrastructure and mobility units, respectively, although Ericsson will have its hands full with Nortel and is known to be uninterested in WiMAX, Motorola’s crown network infrastructure jewel. Cisco could very well use the mobility division, however, which is essentially built on Moto’s acquisition of Symbol, and which has been profitable for the gear-maker.